Boolit deformation at launch and travel down the barrel

[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.
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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:
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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:
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And this is the one that I shot tonight with the new barrel:
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[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:

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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.wordpres...le-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.