Boolit deformation at launch and travel down the barrel

[MBTcustom]

I have been thinking about the "wall" a lot lately. Call it what you will, RPM threshold, Wall, that special place in a boolit's flight where everything turns to poopy diapers, or that thing that can't be named that is to be ignored at all costs......whatever.
I've seen it, youve seen it, even the folks that claim it doesn't exist are beating their heads over it.
The faster you shoot, at a certain point everything goes to the dogs. Some people can shoot faster than others, but at a certain point, the inevitable happens.

It seems that RPM is the force that acts on our projectiles to cause them to go haywire suddenly as speed increases. That's not a limit, it's just a fact of science. Like saying that your tires can take only so much torque until they spin on the pavement. You have as much effect on where your particular boolit quits being accurate as you do on how often your tires squawk.

The thing that I can't get my head around is paper patch and sabots. Seems that I can shoot much faster with those things than I can with a simple GC cast boolit.
Why?!?!?!
Obviously, the patch protects the boolit from something that the barrel does to it, but unfortunately, recovering a soft lead boolit that has been fired at 2400+ undamaged enough to draw conclusions from is a frightfully daunting task! I have tried and tried to come up with a way to do it that doesn't involve me moving to Alaska so I can shoot snow drifts.

However, it occurred to me that shooting at high speed could actually damage the boolit as it leaves the barrel of the gun in ways that you would never detect, even with a HS camera unless you were really really lucky, because the blast would cover up what was happening to the boolit, and by the time the boolit is out of the plume of flame, it's too late to see it.

So, I considered the conundrum. Instead of trying to solve the whole problem, I decided to see if I could just get some clues by "fingering the scale" to my advantage. I thought the most important thing is to recover boolits that had passed through the barrel, propelled by a powder blast, and make sure they were as unmolested as possible. Well, the easyest way to do that, would be to shoot them slow.......like really slow.
I've never messed with cat sneeze loads, so I called Larry Gibson (thank you sir) and he got me lined out in short order.
I loaded up my 30-06 Argentine with a .313 groove (hey it was janky and handy and perfect for my purposes) and loaded up some soft .310 diameter 110gr boolits that I got from milkman last year (thank you sir).
I paper patched a bunch of them, and I loaded a bunch of them on top of 2 whole grains of bullseye, and I fired them into soft, wet clay/sand that I dug from the side of the house.
What I saw was interesting, and I thought I would share.

The rifling smeared the driving bands into the lube grooves and left "fins" inside of them. What's more, they were not even all around the boolits. Even at very low speed, the boolit was not strong enough to center itself in the barrel and was effected in an uneven manner. The thought that I had as I looked at the closeup pictures of the boolits was that it would be very possible for the muzzle blast coupled with the rapidly leaving boolit lube, and also the centrifugal force caused by the RPM to break off some of those fins thereby imbalancing the boolit terribly!
Thus, I wonder if the trip down the barrel sets up a fragile condition but it's at the point that the boolit crosses the crown of the rifle that the damage is actually done to it.
Look at these pictures. One of each groove on one of my recovered boolits:
Think about if those fins were pressed into a lube groove full of lube and then blasted out of the muzzle at high RPM. There would almost certainly be damage to those delicate little features.
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SO what about paper patch?
I theorize that the patch eases the damage to the boolit (this is backed up nicely by the following pictures) which makes it so that material is displaced equally forward as well as backward on the driving bands (no skid effect) and more importantly, acts as a blast shield as the boolit crosses the crown and gas leaks around it. Also, since there is no lube in the grooves, I think it eliminates the effect of hydraulic plucking as the lube leaves the grooves at high speed.
Here's the pictures of one of the paper patched boolits:
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I apologize for the greater damage to the paper patched boolit, but it made a better seal on the barrel and consequently, was fired at much higher speed. Still, the damage is greatly reduced and I think these pictures have shown me something that I couldn't have seen even with a high speed camera.

[bnelson06]

Can you see where any of those "fins" have broken off? I can see where that would cause imbalance. I'm taking it that this is much more complicated than balancing a tire..... Stay with me for a sec. An unbalanced tire will wobble like crazy around 55 mph but evens out when you speed it up to say around 65 mph. Maybe the problem lies in that we can get to that unbalanced stage without "skidding" the bollit it on the rifling but when we try to get past that balance point the boolit doesn't stand up to the forces and basically won't hold the lands to get the rpm into the balanced stage again.

[RickinTN]

Interesting. The "fins" will certainly create an imbalance in the bullet, as will any other "distortion" created by the firing of the round. I was recently asked why I had a certain 30 cal. mold cut with only one lube groove and my thoughts at the time were space limitations (it is for a relatively short-necked cartridge), increased surface area of the bullet in contact with the bore, minimizing possible "accordian" effect on the bullet, and the fact it is a modified version of an already existent bullet which seemed to work well for many. Could it be that a single lube groove on a traditionally lubed bullet would help limit the possibility or opportunity of the "fins" as shown in your pictures? Maybe something else to consider when trying to find the best dynamic fit?
Just some thoughts to kick around.
Enjoyed your post,
Rick

[Love Life]

Polygonal rifling. I've said it before, the cut rifling is a culprit in and of itself. No worries, a walther 308 barrel with polygonal rifling will be headed your way mid-June.

The paper protects the boolit from the knife edge rifling which is actually cutting your perfect boolits.

Look through this thread. You will see example after example of cut rifling...well...cutting bullets. The take a hard look at the boolits fired from Glocks. http://castboolits.gunloads.com/showthread.php?237518-Fired-bullets-photos

Less deformation, no rifling cutting the boolit, and a better gas seal.

[country gent]

Im of the other school of thought on this as cetrifugal effect and balance are at extremes with a rifle bullet. Tim used a 30-06 that probably has a 1-10 -1-12 twist rate at the lowered velocity the diffrent obtration will cause a very slight balance issue at the velocities he fired them at. At full power top velocity loads obtration becomes more so and rpms of the bullet take a big rise. Even the hardest cast bullets are nowhere near what a jacket is and a well formed jacketed bullet is much better for balance. Recovered Paper patch bullets and patches from my 45 - 90 show the pacthes outer layer cut to confetti the inner layer shows heavy impressions but is intact. Base fold is there and unfolded. The base of the bullet that remains shows very light rifling impressions. Possibly impressed thru the paper. This is a bore riding bullet. Bullet recovered averaged 495 grns starting out at 500. This is a slick sided bullet with no grooves.
I found shooting the 243 in a fast twist (1-7) with 115 berger vlds as the throat wore bullets would blow up before 1000 yards. Scorer/ spotter would say the trace would go into a spiral then disappear about 200 yds from the target. I believe the worn throat rpm/ time of flight all contributed to this. The one score was 169 11Xs with 3 misses. I believe these bullets were "spinning " apart.
Theres alot of interesting ways to test this and another interesting "test" would be to check hardness of the bullet before and after firing at full power loads as compression could affect hardness of the base area. Alot of die cast shops casting machines use shot tubes to fill under pressure not only to ensure full fill out but it also makes the material less gummy and soft.
While my 45-90s velocity is only 1200 fps the bullet is very soft. Another thing that comes to mind is the theroy that true paper patched slicks have a slightly higher BC than the same bullet with grease grooves.
Measuring the concentrity of a bullets lube grooves in relation to body before and after firing might be interesting also. What says the lube grooves unsuporrted expand staying centered and true? Or more to one side or the other creating the slight out of balance effect.

[MBTcustom]

I think that it is possible to shoot a balanced boolit out of a barrel, but most of us never think of it that way. I think most of the boolits I shoot look like a dying duck as they exit the barrel. I think the trick to fast and fancy rifle shooting is to use a boolit design that minimizes the effect (that's the assumption I am operating with for the moment).
For instance, one thing I was thinking about is that if I were to use a boolit with a very square lube groove: If I were able to get it started down the barrel straight (Launch) so that it was evenly effected all the way around, the fins would act the same way upon exit. Whether they get plucked off, or if they hold on, the boolit will be more balanced. This is very different from my first thought which was to make driving bands with sharp, scraper style front edges, and long sloping relief. I think that could actually make the problem worse.

The problem with recovering a boolit that was shot any faster than these, is that you can never be sure if what you are seeing is really what you are seeing. What happened when the lube suddenly left the groove? (I say that. I'm going to try some different mediums to stop boolits with and see if I can stop them at higher velocity without damage. Like with crumb rubber for instance.)
See this is what I usually recover from lead boolits fired at high velocity:
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Actually I've spent a long time studying the second picture, but who am I kidding? There's just not enough left to draw any meaningful conclusions from.

[Junior1942]

It would be nice to see high-speed photos of cast bullets at different, increasing velocities at maybe 2 feet from the muzzle. I wasted many hours and many bullets trying to understand why my Turk 38 8x57 shot large cast bullet patterns starting at ~1400 fps. 50 yard groups of 1/2" to 1" suddenly went to maybe 4 feet at 1400+ fps. And the holes in my targets had what can best be described as commas. Obviously to me, the bands were coming off the bullets due to spin. Tim's bullets with their smeared bands would make commas in targets at higher velocities. I was told here that my commas were lube coming off, not bands. Not!

[Nobade]

I am convinced that most bad things that happen to boolits happen as they are leaving the case and passing through the throat. Look at schutzen rifles that use breech seated boolits. By not having to pass through the throat, and being forced to be aligned with the bore before they are launched, they can produce accuracy with soft lead plain base boolits that rifles firing fixed ammunition simply can't produce. Muzzle loaders are another example, even though the boolits have to be smaller than the bore and all sorts of things happen to them at the moment of ignition, they (if made well and good quality) can produce groups that are simply amazing.

Another thing to keep in mind is torque on boolits. My Swede '96 is an extreme example of this, when trying to fire the 175gr. "cruise missile" boolits at high velocity naked with gaschecks, I have had them break in half while in the barrel. My theory is the front half gets spinning before the rear half can catch up, and it twists them apart. But size those things down to bore size and paper patch them, and now they don't break and can be shot at full pressure with great accuracy. The paper is getting spun up by the rifling and transferring that to the core, but the core doesn't see the instant damage the moment it engages the rifling like a full diameter boolit would.

No light on the subject, but a couple of thoughts to throw out there....

-Nobade

[Dan Cash]

A good read/re-read of Mann's "The Bullet's Flight" could help in this discussion.

[MBTcustom]

A good read/re-read of Mann's "The Bullet's Flight" could help in this discussion.

Thanks, I went ahead and ordered it from Amazon.


For the record, im not drawing any hard and fast conclusions from these tests yet. Just experimenting and observing. I still want to find a way to catch a HS cast boolit undamaged. That may be a dream though.
I was considering setting a barrel of crumb rubber at 600 yards to catch a boolit, but then I would have to be sure I could get a boolit in a 12" circle that far away, and I've never shot a boolit that far before.

[gnoahhh]

As I was reading the above posts, I formulated a response that alluded to Mann's "The Bullet's Flight". Glad someone else was on the same track. Dr. Mann (assisted by guys like A.O.Niedner and Harry Pope) addressed these and many other issues 105 years ago, and applied the scientific method to finding the answers. I wonder how many times the cast bullet wheel has been re- invented during the intervening years simply because most people are unaware of this book or haven't read it.

[Junior1942]

....... I still want to find a way to catch a HS cast boolit undamaged. That may be a dream though. ...There is--with a camera. I've seen many photos of jacketed bullets in flight. Exactly none of a cast bullet in flight.

[MostlyLeverGuns]

Heat from the friction of the bullet sliding in the barrel could reduce the strength of the bullet alloy, with increased speed the RPM's increase along with increased frictional heating could weaken the bullet to a point of imbalance or failure. The paper patch may insulate the bullet enough to avoid the heating and loss of alloy strength. A great deal of barrel heating that is attributed to burning powder should be considering the friction of sliding metal surfaces creating a great deal of heat. It is not uncommon in the super high velocity jacketed bullet world for bullets to come apart due to centrifugal (centripetal?) force. Extreme friction and heat is a factor along with RPM. Again the paper patch may provide an insulation layer that keeps the alloy temperature above a critical strength point. ? ?

[MBTcustom]

Im going to be trying to make sense of this and come up with more tests that might make the unseeable seen.
This particular one might or might not amount to a hill of beans, but I'm going to continue on with it.

The above tests were shot with a mil-surp barrel and intentionally undersized and ill-fitting boolits. Since that experiment, I have removed the barrel from that rifle and replaced it with one from a 1962 Remington 700 (it actually passed my white glove test) and I chambered it in the "new" 30XCB cartridge.
I will proceed to shoot well fitting boolits of different styles and recover them.
I'm also going to shoot this rifle in my limited spare time, and run as fast as I can till I find the RPM threshold. I've bought, been given, and traded for a few different 30 caliber molds, so I intend to size and load each of them and observe where the accuracy falls apart.
I expect one of them will outshine the others, so at that point, i'm going back to the cat sneeze loads to see if I can observe a correlation to what I see at high speed.
I'm hoping to use this information to push up the RPM threshold as high as possible. The barrel I am using is a 10 twist (the fastest twist chambered in this caliber to date) so should be a very strict schoolmaster.

I had intended to use an Arisaka chambered in 308 for these tests, and I may still use it in tandem, or to check results from the Argentine.

That's the best I can do (and probably more than I can bite off) for now, and that's the direction I'm going, and the reason for the tests.

[country gent]

Tim Boolits and rifle are capable of the accuracy your wanting 12" @600 yds if everything is right and a solid set up available. Sunday I hit 9 rams at 500 yds missing number 3 just over the back. But that shot was right on my call. Set the pipe behind a mid range target 12" should be same as 10 ring possibly 9 ring. This will give a big enough Black to see at 600 yds. If possible have the range facing north as this gets the sunlight on the target face and easier to see. The issue will be if the sights scope have enough up adjustment for the range with the loads being used. NRA highpower matches course ends at 500 or 600 yds normally. WIth match duplication load 200 - 300 was 3 clicks up and 300-600 was 12 clicks more on the m1as match sight. Hope this infor helps

[tomme boy]

I know it would be really dangerous, but shoot them straight up and recover them into water would be your best bet for recovering a intact bullet.

[MBTcustom]

I know it would be really dangerous, but shoot them straight up and recover them into water would be your best bet for recovering a intact bullet.

LOL! Been there, did the math on that.
First of all, you have no idea what the jet stream is going to do to the boolit, secondly, if you can find one tiny boolit in a random spot in a one mile radius then you're a better man than me, and thirdly, it would be coming down with more force and speed than the boolits that I show in the OP.
Not a good idea at all. might work fine with a wrist rocket and a piece of gravel, but not this.

[Love Life]

what about a zerk fitting and grease to push one through the barrel? That will give an unmolested-ish boolit. What I have seen with recovered boolits is what looks like powder granule indentations on the base as well.

Funky stuff happening to a boolit.

[MBTcustom]

what about a zerk fitting and grease to push one through the barrel? That will give an unmolested-ish boolit. What I have seen with recovered boolits is what looks like powder granule indentations on the base as well.

Funky stuff happening to a boolit.

Not really. If I wanted an unmolested boolit, I would leave them in the box and not shoot them. LOL!

Write it down fellers: every boolit we launch is damaged by the time it leaves the barrel. Every single one of them. I think the trick is to A. damage them as little as possible, and B. damage them as concentrically as possible.

Look at a tire that is perfectly balanced. If you add a 4oz COWW to the rim, you are now unbalanced, but if you add two or more, evenly spaced around the rim, you will still be balanced.
Fortunately, I don't see too many single groove rifle barrels out there, so the object I am going for is to damage the boolit exactly the same with each land that cuts it. If the boolit launches into the the throat with slight pitch or yaw, it will be imbalanced as it exits the other end of the barrel.

[Love Life]

I said "Ish".

[shooter93]

I have some pictures somewhere that Speer bullets had of tests they did with jacketed bullets. They show a spritzer bullet being pushed into almost a round nose shape as it traveled down the barrel. It allowed them to re-design jacket type and material. I've often thought muzzle pressure on a cast bullet does more damage than we think just after it leaves the muzzle too. All tough things to figure out without the right equipment but we all know cast is more fragile to some forces than jacketed and there is no doubt a "paper jacket" helps with these.

[MBTcustom]

we all know cast is more fragile to some forces than jacketed and there is no doubt a "paper jacket" helps with these.

Yeah but we don't understand why.

"Why" as usual, is the most important question.

[W.R.Buchanan]

Every bullet fired is not necessarily damaged but they certainly do change. The idea is to not change them in a bad way.

25-30,000 psi will have it's way with lead and so will 50,000+ psi on a jacketed or solid bullet.. It doesn't even take that much pressure to swage those bullets in the first place. The fact that they are being accelerated at a zillion G's probably has some effect as well.

What everyone has missed is the affects of heat on the boolit. With paper patching the boolit, you are insulating it from the frictional heat generated as the boolit moves down the bore. Where this affects a boolit the most is on the trailing edge which for most intents and purposes controls the disposition of said boolit.

If the trailing edge is altered, (and the only ones that aren't necessarily altered badly are ones with gas checks) then the idea would be to alter them concentrically. To accomplish this they must be introduced into the bore as close to axially true as is possible. You saw the negative effects of this with your undersized boolits. This is also one reason for the "bore rider" type of boolit as long as it fits correctly it eliminates the out of kilter possibility and resultant damage.

I have an NOE 311 299 mould that drops WW boolits at .311 and .2997 which is about as close as anyone is going to get as far as "non interference bore fit" is concerned. It should perform well in a bore of .300. So there is one less variable to contend with. Now, I have to accelerate that boolit in harmony with the barrels harmonics so as to have a minimal effect on the boolits shape.

Your example of the boolits with the lead displaced into the lube grooves is the exact same thing as what happens to solid bullets like Barnes bullets. The material can not compress so there must be a place for the material to move to as the rifling engraves the bullet. This is why these copper or brass bullets all have grooves in them that look like lube grooves.(also controls pressure) By doing the same thing to a lead boolit you alter it less than you would should the event swage the boolit into another shape to cope with the displaced material. IE; less overall distortion. IN the end the boolits material is going to succumb to the law of "path of least resistance." So if you provide a path of least resistance, then you can control the event.

In the end it all this doesn't matter, since what does matter is that you can do the same thing every time. Repeatable results can be coped with, and built on.

Whether or not you can change them for the better is the real issue. Anybody can make things worse!

Randy

[shooter93]

Most likely a myriad of reasons with maybe the biggest being as simple as strength. Tougher jacket does wonders for velocity. Jacketed bullet have pretty soft interiors. Might be interesting if it was possible to develop a much thicker paper jacket that stays on. Or maybe it will be one of the shooting mysteries we never solve....smiles.

[tomme boy]

Myth Busters did a section on shooting bullets up into the air. They recovered a couple and if I remember right the max speed coming down was not very fast. They used a M1 Garand firing full power loads. I always thought that the max speed was around 150 FPS coming down. But it has to come straight down.

[RED333]

Well yall went and done it, now I have a headache.LOL
Good read here, thanks for the info.

[William Yanda]

Would the shooting into a swimming pool as described by Richard Lee work for your bullet trap?
He used it, as I recall, to collect undamaged bullets.
Regards
Bill

[williamwaco]

When you get Mann's book don't just look at the bullets.

He also describes recovering bullets from snow banks then experimented with oiled sawdust when there was no snow.
I seem to remember that the oiled sawdust was completely effective. It takes a lot of it but he describes how to do it.

[MBTcustom]

OK, tonight I took a second to load an XCB with a 311466 and 1.5gr of bullseye powder, and shot it into my sand box. This one was given the typical due diligence that I would give to any cartridge I was loading to full pressure, that is the seating depth was good, the neck was turned with .001 clearance, and it was trimmed to length, and just took enough of the crimp off to allow it to be seated in the chamber snugly.
The result was very even engraving all the way around the boolit (I think. Hard to say because the sand got to it a little).

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I really don't know what to take from these photos. Makes me want to shoot it for real!
Anyway, this was just the first of several sand box tests. I'll post pictures of each boolit as I shoot them and who knows? Maybe there's something to learn here?

[Larry Gibson]

Thanks to goodsteel for some simple yet excellent experiments to get an idea of the potential damage done to cast bullets at the beginning of their entry into the rifling, the journey down the barrel and at the exit. His pictures give us a good idea and while more pictures with much more expensive equipment, perhaps motion pictures and cast bullet damage at higher psi and velocities may provide more information we see, even at the very low psi and velocity, that substantial damage does occur.

Does it matter? Up to a certain point of velocity and with firearms capable of only so much accuracy, probably not. However, as we push the velocity and psi up it certainly does matter, especially when we want the most accuracy possible at higher velocity and psi. Comparing the amount of damage between the naked cast bullet and the PP’s cast bullet is dramatic. Also note the lesser damage to the 311466 because of the narrower drive bands. When we recover a fired jacketed bullet we see the jacket (even the soft steel jackets) compressed inward by the rifling as the rifling does to the PP’d bullet. This causes substantially less damage and disfigurement to the bullet. It is the damage and disfigurement that creates imbalances in the bullets. It is these imbalances that the centrifugal force acts upon when the bullet is in flight causing the bullets to not all follow the same flight path and giving us “groups” instead of one hole.

The analogy of an unbalanced tire is a poor one especially that we can “drive through” the unbalance so the bullet is accurate again. The tire is held by the axle and the weight of the vehicle. There are numerous things that allow it to “drive through” vibration but the main reason is that at a certain speed the is held down against the pavement and the air inside the tire is compressed as the “wobble” hits the pavement. The several things overcome the centrifugal force causing the wobble. The bullet in flight is not held down by anything, the air around it is easily compressed and the centrifugal force is not constrained. While it's thought to be a good analogy and one I've used myself, I was corrected by several individuals in the engineering and physics realm all who were much smarter than I about rotating tires vs bullets.

Many confuse what is referred to as “going to sleep” in the initial part of a bullets flight and stabilization with the affect centrifugal force has on the bullet. The two are not the same and are two completely different aspects of a bullets flight. A bullet can be very well stabilized for flight (point forward) and yet be adversely affected by centrifugal force to a great degree. This occurs with cast bullets (both naked and PP’d) and jacketed bullets. It occurs to naked cast bullets at a lower velocity that it does with PP’d cast bullets and to jacketed bullets. On a historical perspective let us note that when powders and technologies allowed for higher velocities it required PPing to maintain accuracy at those higher velocities. Then when even better powders and better firearm and cartridge technology was developed it required the stronger jacket of jacketed bullet to maintain accuracy at those higher velocities.

Bnelson and RickTN address the issues of the “fins” unbalancing the bullets. That they do when the rifling engraves them front to rear. I have also found (from recovered cast bullets) when cast of harder brittle alloys such as linotype sometimes the back edge of the driving bands are chipped away by the rifling. Of course that imbalances the bullet. With some designs of cast bullets having a single lube groove does help eliminate a lot of the adverse effect of the “fins”. The LBT 30-160 is an excellent example. However, just putting one lube groove on a cast bullet is a too simplistic solution as there are other equally important design considerations.

It will be very interesting to see what Love Life’s polygonal rifled barrel will do. What caliber? What cartridge? What twist?

Country gent gives an excellent dissertation and example with; “Scorer/ spotter would say the trace would go into a spiral then disappear about 200 yds from the target”. What the scorer/spotter was observing was when the bullet began spinning apart the RPM Threshold for that bullet was lowered to the point it began the helical spiral I’ve mentioned numerous times. When the bullet “disappeared” it either completely spun apart or it went of on a severe tangent to the line of flight. I’ve also mentioned that occurrence as a result of a bullet exceeding it’s RPM Threshold numerous times before. Here we “see” and actual observance of the fact……not theory.

Junior1942 has mentioned the “commas” numerous times before. Unfortunately he received some criticism for his observation and reporting of it in past threads. I have to concur with Junior1942 as I also have seen the same thing on numerous occasions, mostly with high RPM cast bullets. Under magnification I see lead smears and not lube on the target surface in those “commas”. This leads me to believe that some part of the bullet, perhaps a “fin”, is forced outward by the centrifugal force of higher RPM. That certainly should have an unbalancing affect on the bullet in flight.

Nobade brings up the very valid consideration of rotational torque and its possible damage to cast bullets, especially considering the longer unsupported bore riding noses of many “modern” designs. When a bullet is accelerated into the rifling it must overcome two vectors of inertia; the 1st vector is forward and the second vector is rotational. A basic law of Physics is that objects at rest tend to stay at rest. In other words the mass of the bullet resists moving forward and rotating. Obviously a faster twist barrel creates a faster/harder rotational torque for a given acceleration rate. In the example Nobade brings up the long unsupported bore riding cast bullet nose used, while being pushed forward by the base and powder combustion in the 1st vector (acceleration), had enough inertia to completely resist the 2nd vector (rotational torque). The result being the bullets twisted apart in front of the first driving band. The obvious conclusion here is the inertia of long unsupported bore riding noses at higher acceleration in faster twist barrels can and does cause damage and/or resultant unbalancing to the cast bullet. This is why I find cast bullets with shorter nose and longer bearing surfaces can be driven to higher velocity before reaching their RPM threshold. The 311466 goodsteel shows is an excellent example of a well designed cast bullet; short nose, long bearing surface and multiple shallower lube grooves with narrower drive bands.

A couple other good points brought up is the heat generated on the bullet and the strength of the bullet. Heat is indeed a factor and how to control it with a naked cast bullet is the question. I am of the opinion (only that as I’ve no facts per say to base it on) based on observation that the multiple lube grooves of Loverin designed cast bullets filled with lube also insulate the bullet from a lot of heat from friction during the internal ballistic phase. As to strength of a naked cast bullet I’ve found a softer malleable alloy of mid BHN (18 – 24) is more accurate at higher given acceleration rates than is a harder brittle antimony rich alloy such as linotype (especially when HT’d) .

It’s been a while since I read Mann’s book but, as I recall, he was not pushing the cast bullets above the RPM threshold. Thus his, none the less, very fine work is lacking in that regard. Anyways, just my own two bits of comments regarding this very interesting thread.

Larry Gibson

[MBTcustom]

You know, another thing I noticed (along the lines of boolit deformation) was the narrower lands in the new Remington barrel as opposed to the broader ones in the original.
From a manufacturing point of view, this would be much more challenging to accomplish, but the merits are easily seen in the reduced boolit distortion.
That's about all I was able to see in the last pictures.
Thanks for weighing in Larry, and thanks again for all the advice on cat sneeze loads!

[Nobade]

I haven't tried it yet, but it would be interesting to compare identical chamberings in a conventionally rifled barrel and a 5R form one. I have been installing a lot of Bartlein 5R barrels for people and they all love them. Say they are incredibly accurate and also clean up easy. Anybody here shot any boolits through one yet? The round edges on the lands and asymmetrical 5 grooves MIGHT be a real boon to us casters.

-Nobade

[kens]

I would like to weigh in on a comment, if I may.
We all heard of heat, friction, pressure on the boolit going down the barrel.
I have a "what if" scenario to be presented as a question.
What if the heat/friction/pressure was enough to molten the thinnest surface of a boolit.
If, you had a thin layer of molten metal on your boolit, then as it leaves the muzzle, that molten would get 'thrown off' and in random ways.
I am thinking that a small bit of molten lead gets thrown off as boolit exits the muzzle, and that is a very un-consistant thing.

[MBTcustom]

I would like to weigh in on a comment, if I may.
We all heard of heat, friction, pressure on the boolit going down the barrel.
I have a "what if" scenario to be presented as a question.
What if the heat/friction/pressure was enough to molten the thinnest surface of a boolit.
If, you had a thin layer of molten metal on your boolit, then as it leaves the muzzle, that molten would get 'thrown off' and in random ways.
I am thinking that a small bit of molten lead gets thrown off as boolit exits the muzzle, and that is a very un-consistant thing.

I don't know why it would be inconsistent. In fact, the only thing that is inconsistent in the whole firing process is the process of getting the boolit into the barrel. I think once the tail of the boolit crosses the throat of the rifle, whatever will be will be. It's the deformation that happens in that time of low support and high stress and torque that sets up a condition that the muzzle pressure, RPM, muzzle pressure, and wind can all act on to make the boolit shoot terribly.
I'm fast starting to think that no single factor has as much effect on an improperly damaged boolit as RPM, but that's not the primary discussion here. I'm trying to figure out how to get the boolit launched, engraved, torqued up to spin, and down the barrel as cleanly as possible.
There's no way to eliminate the damage to the boolit, but there must be a way to damage it in a controlled and concentric way.
Observe these next boolits that I fired tonight. Look at the deformation and how different lube grooves set up a more accurate situation (or not as the case may be.)
First there are two spitzer boolits that I bought from littlewolf (thank you sir!)
It bears mentioning that all these boolits were sized in the same die (.311 Star sizing die bought from lathesmith. Thank you sir!) so don't get the idea that some of the deformation is from a larger boolit. They are all the same size, and they are all about the same hardness and alloy.
104930
104931
104932
104933
Interesting eh? The results are startlingly different from the 311466 up yonder!

This next one is a mold that I traded Geargnasher for (thank you sir!) This is the 173gr 30SIL from MP molds. Look how the deeper lube groove takes the pressure off the trailing fin so that it is more robust. Unfortunately, that trick only worked on the first driving band, but the proximity of the second driving band to the gas check seems to provide a bit of protection to the fragile fins that are rolled down there. Very interesting:
104935
104936
104937
104940

Finally, I shot the little 110 grainer again to see what the differance would be between the old barrel and the new one.
This is the one that was shot with the old barrel:
104939
And this is the one that I shot tonight with the new barrel:
104938

[Love Life]

The round edges on the lands and asymmetrical 5 grooves MIGHT be a real boon to us casters.

-Nobade

Probably.

[MBTcustom]

BTW, I keep meaning to touch on this, but I'm dying to see what Poly rifling will do for cast lead. So just get a barrel together there LL and we'll find out directly!
You still dreamin in 338? LOL!

[Love Life]

Dig this:

104941

Now, which one do you believe will be better on a boolit? According to the gospel, a polygonal rifled barrel also provides a better gas seal. That's good right? My theory is that a polygonal rifled barrel will be easier on the boolit while in the barrel and provide a better gas seal which should be Mo' Betta.

I am not afraid of polygonal rifling and lead boolits. As soon as I hear back from Walther, everything should be good. Leade time might be around 8 weeks.

Now if someone can DISPROVE me with REAL WORLD INFO before I embark on this journey, I would very much appreciate it. However; "I heard this one time" simply isn't going to cut it. If it works, then I'll be incredibly happy. If it doesn't then I'll just shoot jacketed out of it. Oh, and the walther 30 cal polygonal rifled barrels are .298 lands and .307 groove per Walther. Should allow me to be in like a dirty shirt with .309 boolits.


I'll bow out at this point to avoid off topic clutter, but I'll have my answers this year.

[MBTcustom]

I think a poly rifle barrel would be Das Boot, but never messed with it m'self.

[Any Cal.]

Poly rifling probably good, but nobades experience with torque makes me wonder if poly would be best with slower spin-up, to keep from skidding on lands, as it looks to be a less positive drive.

What you need is a medium bore Paradox set-up with poly rifling for the best of all worlds. Then shorten the barrel to slow down the rpm rather than slow the velocity if necessary.

[Love Life]

Dig this: http://precisionrifle.files.wordpress.com/2014/01/excerpt-on-schneider-barrels-and-p5-5p-polygonal-rifling-from-david-tubbs-the-rifle-shooter.pdf

Seems more velocity with less powder as well. Lower pressures should also help. The possibility of "Jumping" the rifling is an interesting one.

To answer Mr. Gibson- It will be a 1 in 12 chambered in plain vanilla 308. I need to hit some mould catalogs for a good boolit. I do not have much faith in a long nosed boolit, so I want a squat boolit if that makes sense. When I look at the bore riders, I think of a roll of play-doh spun in the hands. Spin slowly and the roll of play-doh is fine. Spin it fast and the end of the roll starts whipping around all nimbly-bimbly. That's the best way I can describe it.

[Nobade]

Also consider what Micro-Groove rifling does with boolits. Even drive all the way around and very minimal distortion of the boolit. Veral Smith had something to say about that in his book, essentially comparing it to a spline drive socket rather than a 6 point one. I know all the past problems with micro groove, but it is because people didn't understand that the bore is intentionally large on those barrels so the grooves can be the right diameter but move less metal around. Too bad high quality micro groove barrels aren't available to test, at least not to my knowledge.

-Nobade

[Larry Gibson]

Dig this: http://precisionrifle.files.wordpress.com/2014/01/excerpt-on-schneider-barrels-and-p5-5p-polygonal-rifling-from-david-tubbs-the-rifle-shooter.pdf

Seems more velocity with less powder as well. Lower pressures should also help. The possibility of "Jumping" the rifling is an interesting one.

To answer Mr. Gibson- It will be a 1 in 12 chambered in plain vanilla 308. I need to hit some mould catalogs for a good boolit. I do not have much faith in a long nosed boolit, so I want a squat boolit if that makes sense. When I look at the bore riders, I think of a roll of play-doh spun in the hands. Spin slowly and the roll of play-doh is fine. Spin it fast and the end of the roll starts whipping around all nimbly-bimbly. That's the best way I can describe it.

Probably about as good an analogy as any as to what happens to long bore riding noses and the unsupported spritzer noses. I might suggest you take a look at the 30x57 cartridge oodsteel is chambering cartridges in, if you have the action length (3" cartridge oal). It has a bit more case capacity than the .308W and it has the '06 length neck. Easy to make cases and easy to modify standard '06 dies to load with. The longer neck allows the LBT 160 or the 311466 bullets (the 2 best choices for HV as both are "squat" with short noses and long bearing surfaces) to fit the longer '06 length neck perfectly. Otherwise to keep the GC inside the .308W case neck and have any cast bullet over 140 - 150 gr you'll need a longer free bore in the throat or a bore riding nose designed cast bullet. Just a suggestion as the 30x57 was designed with that in mind. You might also consider a 13 or preferably a 14" twist.

Larry Gibson

[Love Life]

Hmmmm. I've got a medium length mauser action floating around I could use. A 13 or 14 twist might not be good for me though. If the cast boolit thingy is a no go, then I still want to be able to shoot 175 SMK from the barrel. I am off to reread the 30X57 thread.

[Dan Cash]

I know it would be really dangerous, but shoot them straight up and recover them into water would be your best bet for recovering a intact bullet.

General Hatcher tried that with less than sterling results. The wind and ballistic drift seem to take the bullet to parts unknown.

[Larry Gibson]

Hmmmm. I've got a medium length mauser action floating around I could use. A 13 or 14 twist might not be good for me though. If the cast boolit thingy is a no go, then I still want to be able to shoot 175 SMK from the barrel. I am off to reread the 30X57 thread.

Good plan. You might also consider a longer barrel as the 13/14" twist barrels are usually "Palma" barrels and come in several contours of 26 - 30"+ length. My current Palma barreled .308W has a 27 1/2" barrel and when I build my 30x57 I will have a minimum 28" barrel to start with (Light Palma contour) but preferably a 30" finished length. I'm wanting a 16" twist in mine as I've no plans on shooting any bullet heavier that 165 gr with mostly the 311466 or LBT bullets in mind. If I find that length barrel unwieldy then I can always removed an inch or two. Hard to add length to a barrel though. The 14" twist Palma .308W barrel is doing quite nicely with 311466s at 2600 fps but it's short on case capacity to push that bullet faster with slower burning powders. It also appear the RPM threshold is right around 2650 fps with the .308W, 311466 and a compressed charge of AA4350. The psi runs around 42,000 with that load (measured with Oehler M43 in that rifle). With the increased case capacity of the 30x57 and the longer 16" twist barrel I should push 2800 - 2900+ fps with 100% load density, psi under 40,000 and still be under the RPM threshold.....that is the plan anyway. Finding a barrel has been the problem.

Larry Gibson

[35remington]

One of the best "mediums" I've used for recovering bullets undamaged is......the dacron in old sofa cushions, you know, the big ones you lean against that are part of the furniture. We'd stack a number of these cushions together and the bullet would "snag" progressively more fibers as it went through the cushions, eventually stopping in about an 8 to 9 foot thickness. I'm sure bluntnosed bullets snag fibers better than the pointed shapes, but all eventually would snag.

The deceleration is quite gradual and due to the many fibers, rather "cushioned" if you don't mind a bad pun. Some diligence at dumpster diving and a little time could turn up a number of these cushions, and then the test is on. At the time we were looking at forcing cone skidding in 357 revolvers, but it works on rifles, too, given enough cushions and dacron.

[kens]

Good plan. You might also consider a longer barrel as the 13/14" twist barrels are usually "Palma" barrels and come in several contours of 26 - 30"+ length. My current Palma barreled .308W has a 27 1/2" barrel and when I build my 30x57 I will have a minimum 28" barrel to start with (Light Palma contour) but preferably a 30" finished length. I'm wanting a 16" twist in mine as I've no plans on shooting any bullet heavier that 165 gr with mostly the 311466 or LBT bullets in mind. If I find that length barrel unwieldy then I can always removed an inch or two. Hard to add length to a barrel though. The 14" twist Palma .308W barrel is doing quite nicely with 311466s at 2600 fps but it's short on case capacity to push that bullet faster with slower burning powders. It also appear the RPM threshold is right around 2650 fps with the .308W, 311466 and a compressed charge of AA4350. The psi runs around 42,000 with that load (measured with Oehler M43 in that rifle). With the increased case capacity of the 30x57 and the longer 16" twist barrel I should push 2800 - 2900+ fps with 100% load density, psi under 40,000 and still be under the RPM threshold.....that is the plan anyway. Finding a barrel has been the problem.

Larry Gibson

That kind of reflects what has been said by Veral Smith at LBT.
He says you can drive lead bullet either high velocity, or, high pressure, but not both.
In this case you are looking at hi velocity on low pressure, and that is suppose to work.

[MBTcustom]

Really excellent information there Sgt.mike.
I'm still trying to make sense of the whole groove % thing. I would think that more groove is better even though thinner lands would get shot out quicker, but with lead, I would think thinner is better. Like get a barrel that is 75% groove?
Looking at the dramatic difference between the military barrel and the 60's Remington, It appears that the lands on the military barrel are about .070 in width, where the Rem is .042 or something (just eyeballing with calipers here). The Remington caused less distortion to the boolits. I'm going to load up a few Sunday and see if I can giver 'er a try.


BTW, my copy of "The bullet's flight" just arrived yesterday. Should be a good read.

[tomme boy]

I was always told the 2,3,4 grove barrels were made to last longer in the throat before burning out. That was the reason behind it, not the cost savings. I know they are harder on bullets. They tend to blow up the jackets when pushed fast.

How would the cost of a barrel be lower with a two groove over a 5 or 6? They have to pull or push a button so that would be the only cost difference is the cost of the button.

[MBTcustom]

I was always told the 2,3,4 grove barrels were made to last longer in the throat before burning out. That was the reason behind it, not the cost savings. I know they are harder on bullets. They tend to blow up the jackets when pushed fast.

How would the cost of a barrel be lower with a two groove over a 5 or 6? They have to pull or push a button so that would be the only cost difference is the cost of the button.

Well, first, I would think that 2 3 and 4 groove barrels would be harder on a boolit, only if the grooves were very narrow creating large/wide lands that deform the projectile more?

Second, barrels used to be all cut rifled. In that process, each groove was cut into the barrel with a single hook cutter. It took about 20 passes per groove if you were "gettin jiggy wid it" and they certainly were (Id be willing to bet that in war time production they were getting it done in less than 10 passes per groove). Obviously, a reduction in the number of grooves cuts time off production dramatically.
As I understand it, pulled button rifling didn't really gain widespread acceptance until the 50's?
I'm not saying anything else as Sgt.Mike and Larry Gibson are about to make me look like an idiot, but that's my shaky understanding on why less grooves would make faster production.

[Col4570]

It would seem that a naked Boat Tail Bullet might reduce the drag,or at least place it neatly at the Boat Tail.The problem then would be transferred to the lack of lubricating grooves.This might be reduced by using a lubricated wad and Card.I am thinking on the lines that the drag is made in each groove and that a n area to deposit the drag might help.I think the problem is unsolvable with cast bullets.

[Larry Gibson]

Yes the reason the 2 groove barrels came about in the M1903A3 was as stated; "the whole exercise was to reduce production time with a acceptable accuracy level". We have to also remember the oft quoted Remington test of the accuracy was more of a "demonstration" to allow them to save production time. Of course the 2 groove barrels were going to prove as or more accurate that the current production 4 groove barrels. That's the way those "demonstrations" are ran. Having conducted considerable testing of numerous 2 groove M1903A3 and M1903A4s against 4 groove barreled M1903/M1903A1s I found that with quality jacketed bullets the 4 groove barrels showed an accuracy edge beginning in the 500 - 600 yard range. With cast bullets the 4 groove barrels had the accuracy edge at 300 yards most often. The reason I surmise is bullet distortion/imbalance is less and more asymmetrical than with the 2 groove barrels. Now please don't anyone begin posting nice 100 yard groups from 2 groove barrels. Yes they can shoot nicely but they are not more "cast bullet friendly" as the myth goes. Fact is if the 2 groove barrel were more accurate the benchresters and HP shooters would be using them. The factories would also be making 2 groove barrels. They are not.....there is a reason and it should be obvious.

Please, I wish the RPM Threshold would not be referred to as a "wall". It is not a "wall" as that gives the notion you can not go beyond it. We can easily shoot beyond the "wall" both with velocity/increased RPM and with usable accuracy. It is named the RPM Threshold because you can cross the threshold and still continue with higher velocity and some semblance of accuracy. The RPM Threshold is simply that point where accuracy will begin to deteriorate. To what degree depends on numerous variables. One of which is the very topic of this thread; "boolit deformation".

Fact; If the naked cast bullet is going to be at all accurate it must engage the rifling to spin it adequately for stabilization and that engraving by the rifling is going to cause deformation.

We know we can control the deformation to a degree because of the difference goodsteels experiments here are showing. We can do this not only through design of the rifling (number and shape of the lands and grooves), by the composition of the alloy, the design of the cast bullet and the rate of acceleration. I am of the opinion that there must be an asymmetrical balance between the number of grooves, the depth of the grooves and the width of the grooves. We also know the "grip" of the rifling on the cast bullet must be sufficient to prevent skidding/stripping during acceleration. For a given twist the faster we accelerate (both with a faster time/pressure curve and a higher velocity) the better the grip on the cast bullet the rifling must have. Ergo the problem with HV cast bullets; the higher the velocity the better the grip must be resulting in more distortion/imbalance of the bullet. A vicious circle, eh?

Thus we must balance all the various variables to succeed. For example; In my quest for a .30 cal barrel with a 16" twist (finished length of 30") I am looking for a 4 groove barrel with equal land to groove width having 50% of each or a 3 groove barrel also of equal %. I'm want the bore to .300 and groove depth to be .004. Might be a bit much but remember I am going to push upwards of 2900+ fps so the rifling must be able to hold the bullet w/o any stripping or skidding. Those are my current thoughts anyways.

Larry Gibson

BTW; didn't the 7.7 Jap have Metford or polygonal rifling? Been many years since I've shot one (still have the dies) with cast bullets but as I recall I didn't push cast bullets much beyond the RPM threshold with any degree of accuracy. That was way before I understood about the RPM Threshold and I don't even have any notes of what I did. I'd almost bet I was using an old Ideal 311284 mould I have that dropped the bullets cast of #2 alloy at .314 - .315.

[Love Life]

Check is in the mail, so I'll get to test the poly theory in about 10 weeks.

I've been thinking about what Nobade said about torque twisting one of his boolits in half. I wonder if you can "cheat" that with a gain twist?

[W.R.Buchanan]

With cast boolits I totally agree that the lands and grooves should be the same size. My Remington 03A3 has a two groove barrel and the lands and grooves appear to be the same width. Also the bore is in fact .300 and the grooves are .004 on a side yielding a .308 groove dia. My NOE 311299 drops WW boolits at .311 and .2997, so sized to .310 and the nose left alone should yeild nirvana.

If I was going to replace that barrel I'd be looking at a Criterion barrel with 4 grooves and the same "symmetrical" relationship of equal width lands and grooves.

I don't know if there is a real reason for this relationship, but it just seems logical.

I know all of you remember when you were in grade school and the teacher asked you how much 40 divided by 10 was, and you said 10 and then she asked you how you got there and you said you just "knew that was the answer." and then you got flunked for not showing your work.

Well,,,,sometimes you just know what is right.

Randy

[MBTcustom]

With cast boolits I totally agree that the lands and grooves should be the same size. My Remington 03A3 has a two groove barrel and the lands and grooves appear to be the same width. Also the bore is in fact .300 and the grooves are .004 on a side yielding a .308 groove dia. My NOE 311299 drops WW boolits at .311 and .2997, so sized to .310 and the nose left alone should yeild nirvana.

If I was going to replace that barrel I'd be looking at a Criterion barrel with 4 grooves and the same "symmetrical" relationship of equal width lands and grooves.

I don't know if there is a real reason for this relationship, but it just seems logical.

I know all of you remember when you were in grade school and the teacher asked you how much 40 divided by 10 was, and you said 10 and then she asked you how you got there and you said you just "knew that was the answer." and then you got flunked for not showing your work.

Well,,,,sometimes you just know what is right.

Randy

Yeah, even a blind hog finds a grain of corn sometimes.
For 18 years I have been hoping my "gut feeling" about firearms would render small groups at long range. So far, I have had only one day in the sun where the first load I took out with a new rifle was actually exactly what it really wanted to shoot. I was shooting 1/2" groups at 200 yards first rattle out of the box. However, it was one of those times where I had just thrown some loads together to go fireform some brass, so I didn't write down the charge or the COAL [smilie=b:
Other than that one time, accuracy with jacketed or cast has been the result of careful experimentation, research, and documentation.

I'll tell ya one thing that I took from this testing though: I'm going to be shooting the 311466 and the 30 SIL in this rifle.

[Any Cal.]

Sorry, when I mentioned a Paradox bbl earlier I was remembering it as a gain twist, but rather it was partially rifled...oops! In any case, in reading about them just now, it was said that the slower (1:36) twists imparted more spin to the slugs that were moving faster (1200fps) than the faster twists (1:24). The faster twist came into its own with the slower (1000fps) velocitys.

Makes one wonder how much or little gain twist would be advantageous, as on the one hand, these slugs were hitting rifling at full speed and being forced to spin,but on the other, at 1k fps more twist was better. Apparently it was confirmed that skidding on the lands is what reduced the spin on the slug. Just food for thought.

It makes me wonder what the name of the gain twist barrels they built 150 years ago were actually called...

[MBTcustom]

Tim,
What about me dropping off the 721, you taking some commerical cases that I have around here, modifying them for cat's sneeze and trying out that barrel. It is a 1-10 twist but the groove's might be differant as the 721 was made in the 50's, we both have seen the wear in the throat. Then do a comparision for giggles might not produce any differant results, or may just be jaunky enough to discount. I dunno but it is a offer. Just measured the Cerro safe casting 6 groove, .050" land width, .115" groove width, groove dia is .3085" on the 721 barrel


No problem Mike. That will be $149.95 with your military discount and the good buddy discount. Cheap enough right?
:kidding: