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.
Attachment 104725
Attachment 104726
Attachment 104727
Attachment 104728

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:
Attachment 104729
Attachment 104730
Attachment 104731
Attachment 104732

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/show...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:
Attachment 104757
Attachment 104758
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".