Soft Boolits

[bobk]

I was just rereading an article by Paul Mathews on why he favors the soft lead paper patched boolit for hunting, he claims that he's pushing near pure lead maybe 2000 fps. I've read this other places, too. OK, what I've been thinking of doing is using 50/50 WW/Pb, maybe with some tin, in GC boolit designs. Now, the question is, I've read repeatedly on this forum, and others, that there are velocity limits depending upon the hardness of the alloy. Yet when we throw a thickness of paper of maybe .005 between the boolit and the barrel, this limitation goes away. This doesn't make much sense to me. The paper keeps the lead from being abraded off by the barrel, but the lead boolit still has to engage the rifling firmly. With a GC to protect the base, shouldn't we be able to use nearly pure lead for hunting boolits? The softer lead should even allow a bit of "bump-up" to fit even better. Explain to me why I'm full of it, please.

Bob K

[Larry Gibson]

The PP provides 100% support around the bullet in the bore during accelleration. This prevents (up through 1900-2000 fps, particularly in slower twists) unwanted uneven set back and obturation. Thus the bullet exits the barrel with less defects (unbalances) and is then more accurate. You don't have this support around a regular cast bullet. At higher accelleration the softer the alloy the more the nose sloughs off to one side, the more the lube grooves collapse and the more the base can get swaged uneven. All of this makes for an unbalanced bullet, the greater the wobble and yaw will be on exit and the more inaccurate the bullet will be.

Larry Gibson

[bobk]

Larry,
Still trying to get my head around this. The nose slumping bothers me, because of softnose (two alloys) boolits working.

What does occur to me is that if lube grooves collapse, then maybe what we are dealing with is a too-large boolit or one that has been sized too much. It would be interesting to know HOW the grooves collapse. Does it happen in a plastic manner, or are they fracturing due to the antimony in most of the alloys we use?

Bob K

[felix]

Ideally, it would be in a plastic manner 100 percent. However, that never really occurs because scraping/shearing occurs too. Minimizing the latter is the objective. So, we live with the best ratio we can obtain using the skin in use. What happens to the lube grooves doesn't really make any difference provided all differences are equal all around. ... felix

[Slowpoke]

There is a excellent article concerning lube groove collapse by the late Merrill Martin in the CBA Cast Bullet Journal # 133 May- June 1998 and #134 July- August 1998, it is a reprint of a article he did for Precision Shooting mag. 12-87 and 2 -88.

He didn't leave any stones unturned!

good luck

[Boerrancher]

Lots of good info here in this thread. The alloy of my choice for hunting is a 50/50 WW and pure mix. I very seldom add any tin unless I have trouble with fill out. I don't have any problems with speeds of 2300 fps. I also make my own gas checks though that do most of the work and helps eliminate some of the problems mentioned above.

Best wishes from the Boer Ranch,

Joe

[longbow]

While I was doing some penetration testing of boolits out of my .44 mag Marlin I recovered some Lyman 429421's that had collapsed at the lube groove. I was surprised at how badly deformed they were and the load was not that hot. Alloy was largely air cooled range scrap (mostly hard cast pistol boolits).

There must have been enough pressure/acceleration to cause the smaller cross section at the bottom of the lube groove to yield. They do have a pretty large lube groove so smaller cross sectional area there.

I have photos if you are curious.

Longbow

[leftiye]

Funny thang, Cast grease groove boolits also shoot fine when paper patched. Shouldn't be any less fore shortening or slumping with the paper patch than without it. EH? (unless the lead were for some reason harder due to the paper patch, and the boolit being cooler because of the patch insulating the boolit maybe. Ya think?) Actually, if you accelerate the paper patched boolit to a higher velocity (should be higher pressure?), there should be more slumping, both of the nose, grooves, and the base.

[bobk]

Boerrancher,
That is exactly what I want to do, 50/50 and about that speed. the two calibers that interest me the most are .30 and .40, namely the .30-30, and the .405 Win. I'm hoping for a less than bitterly cold winter so I can begin experimenting after deer season.

longbow,
I don't doubt you, I'm just having trouble visualizing what happens.

leftiye,
Yeah, that bothered me, too. Sounds like I've got a winter's worth of experimenting to do.

[longbow]

bobk:

Take a look at the attached photo. While not the best picture you can see pretty clearly that the boolit on the left is shorter and fatter than the boolit on the right. Also, if you look at the lube groove it has collapsed and unevenly at that ~ the right side has filled out to the rifling.

In fact both failed and if the photo was clearer you would see wrinkling in the bottom of the lube groove on the right hand boolit.

Pressure was too high for the strength of the alloy.

Even if paper patched the boolit would have failed at the small cross section. I am pretty sure what Larry means is that a full length paper patched boolit is well supported along its length in comparison to a nose bore rider which is partially supported by the lands (if it touches) or semi spitzer which would be even worse. Correct me if I am wrong there Larry but that's my take.

Also, most paper patch designs do not have lube grooves and if they are grooved the grooves are very shallow so not as much reduced cross section.

Longbow

[bobk]

longbow,
I think I can see the wrinkling you're talking about. Hmmm. I wonder if even a small amount of COW would cushion the initial pressure on the boolit base and reduce this tendency.
Bob K

[stocker]

longbow; I would question when the collapse occurred. Do you think it is doing it while in the bore or is it occurring on impact? Looking at the nose damage I would guess it's happening on impact as the base drives forward under momentum. Pretty hard to determine unless you can shoot a bullet that exhausts it's momentum in a medium that does no damage to the boolit.

[45 2.1]

Take a look at the attached photo. While not the best picture you can see pretty clearly that the boolit on the left is shorter and fatter than the boolit on the right. Also, if you look at the lube groove it has collapsed and unevenly at that ~ the right side has filled out to the rifling.

I've dug up several thousand boolits to observe what was happening to them. The uneven collapse indicates it didn't get launched straight or was undersize. Anything that was big enough, even when cast of pure lead and shot at higher pressure to make it fail, did not do this. Undersize boolits did though.

[44man]

I have heard complaints from BPCR shooters about off center nose slump with the Lee 459-500-3R boolit, at the miserly velocity in the 45-70.
Shoot a dead soft boolit out of a revolver and I don't care how it fits or straight it enters the forcing cone, if started too fast it turns into a blob of putty before it goes down the barrel. Out of time cylinders just make it worse but it will not cure this if in perfect time.
Of all the .38 S&W revolvers I cleaned for the police dept, most had lead on the OUTSIDE of the cylinder, in the throats and in the frame opening along with packed rifling. Lead turned to putty would squirt out of the gap.
For those that believe in "Bump up", how much more perfect can you do that?
Take a pure lead boolit and smack it with a little tack hammer, now what does 15,000 to 30,000 psi do? Then to shoot the soft boolit at 60,000 psi sure doesn't sound very good.
Boolit design and alloy are the two things that allow us to shoot faster. The trick is to get expansion on game at fast velocities yet have the boolit maintain integrity in the gun.
I had a rude awakening with my 45-70 revolver over the last few seasons when I found even a hard WFN does LESS damage to deer when it is sped up. The pressure wave in front of the boolit is forcing lung tissue away from the boolit. I must make the nose softer to expand and slow it down inside the deer so it does some work. There is going to be a limit to overall boolit softness so I don't ruin it in the gun or skid rifling the full length of the boolit.
It seems to me the problem was solved long ago when they wrapped a boolit with a gilding metal condom and started to call them bullets! :mrgreen::mrgreen:
The point a lot of you forget is when soft lead is shot too fast it will not take the rifling right away and will tend to try and go straight. Then when someone asks about leading in front of the chamber or in front of the forcing cone, the standard answer I read is that the lube is not working. Well, doesn't lube just make a boolit more slippery?
Won't a paper patched boolit have more friction?

[Larry Gibson]

Longbow

It has to do with inertia and that lead is elastic. Objects at rest tend o stay at rest: the pressure is exerted on the base of the bullet when the cartridge is fired. The front of the bullet wants to stay at rest while the rear is pushing forward. The front of the bullet also is engaging the lead first and beiing swaged down to groove size thus the coificeint of friction is higher at the front of the bullet...basically it is being held back. If the elasticity of the alloy is not enough the bullet gives at its weakest points. Thos are in the thinner parts of the lube grroves, a base that is not thick enough and a nose that is not supported. Years ago I shot quite a few bullets, cast and jacketed, into a bullet trap at a crime lab. On the cast bulleys you could definately see where the bases had swaed, bumped up or whatever unevenly, where the lube grooves had collapsed and where the noses had slumped to one side. The bullets were all at over groove diameter so they were not undersize. The higher the pressure and/or the faster the time/pressure curve (accelleration) the more this happens.

The PP supports the bullet along its entire length and also has a lower coeficient of friction. Thus I beleive the front of the bullets move ahead more readily into the barrel without the resistance as with the regular cast bullet. Thus given equl alloys they sustain less set back and can be driven to higher velocity with accuracy than a regualr cast bullet.

Larry Gibson

[44man]

Larry, thank you--SPOT on.
But we need to discuss the paper patch versus the lubed boolit more. I have no experience with paper patching but feel it grabs the rifling faster. The paper can't add support in any way or strengthen the boolit. But it seems to me that paper might have more friction and wear the bore more too. Like a cloth patch in a muzzle loader will polish a bore until it quits grouping and needs etched.

[longbow]

Larry's got it right.

The boolit base is pushing the rest of the boolit. When it gets whacked in the butt it tries to move imediately but the mass of the rest of the boolit is not wanting to move ~ inertia. The stress is highest at the base of the boolit and diminishes along its length until it is 0 right at the nose.

The small cross section at the bottom of the lube groove is very near the base so sees very high stress. An alloy that is not hard/strong enough will yield.

The photo is not very good but rifling impression is all down the right side so this yielding definitely occurred in the barrel not at impact.

While I think Larry has a good point with the nose friction and engraving forces which certainly do resist forward motion even more, personally I suspect that even paper patched this alloy would have failed at the lube groove due to insufficient cross sectional area for the strength of the alloy and pressure of the load.

Maybe I see another test on the horizon: try paper patching some of these boolits of same alloy at same load to see if they still collapse at the lube groove. I would have to either size them down to paper patch or make up an "equivalent" boolit of correct size.

I agree with 44man on the "not taking the rifling right away" comment too. I have recovered cast boolits shot from my .303 British which has even width lands and grooves. Some of the recovered boolits show wider "grooves" (from the lands) and narrower "lands (what was in the grooves) due to that very effect. The boolit was too soft for pressure/acceleration and did not want to start spinning right away so almost stripped in the rifling. Again, inertia at work.

An object at rest tends to stay at rest, an object in motion tends to stay in motion.

Longbow

[Black Jaque Janaviac]

I think you fellas are forgetting the differences in strength of lead vs. paper. Pound one of your boolits down into a lead sheet 0.003" thick then compare to a sheet of paper as far as:

Compression strength
Tensile strength
Shear strength

I think you'll find that paper wins against even the hardest alloys.

Keep in mind that the stresses put on a paper jacket are along the length or circumference of the jacket which is in favor of the paper. A .45 bullet is almost 1 1/2 inches in circumference. The torque applied to the jacket is like trying to shear a sheet of paper 1 1/2 inches thick. That's about the thickness of our phone book and I can't tear it in half.

Plus there may be something in the combination of soft lead and paper that reaps the best of both worlds that a plain cast bullet cannot do. The softer lead bumps up more easily to prevent gas blowby, yet the paper bears the brunt of the shear stresses of the rifling.