Lead bullet pressures are greater than jacket bullet pressures of the same weight

[Larry Gibson]

JonB_in_Glencoe

> We know that as the pressure increases in a ladder test of castboolit loads, the amount of obturation to the castboolit increases.
> As that obturation increases, I suspect that friction increases.

Yes, that is what we've always been told and we've heard it so often it's become "what we thought". But do we really "know" that? Or are we just repeating and believing someone else's assumption? Obturation is defined as swelling to close or obstruct. If our cast bullets are .001 - .003 over groove diameter are they swelling to close? No they aren't. The cast bullets we shoot almost always are over groove diameter. Truth is they are swaged down to go through the barrel. Additionally with lubed bullets they are swaged down to ride on a layer of lube. Thus there is no frictional contact between the alloy and steel. Also the lubed cast bullet is swaged down within one length of bearing surface and begins riding the lube within that one bearing surface of travel. There is no "friction" between alloy and barrel after that. Yes, old BP bullets were dependent on swelling to close and were supposed to obturate as those bullets were smaller in diameter than groove diameter. The over groove diameter bullets we use today do not "swell to close".

Conversely. the jacketed bullet also can be swaged down or even truly obturated if undersize and remains in contact with the steel throughout its travel in the barrel.

Over 12 years ago after I began broaching the subject of the adverse affect RPM had on cast bullets or even jacketed bullets I began serious testing to find out. I received a lot of criticism with "bbbbwwwwaaaahahahaha you changed what you said....." commets from numerous knowledgeable people here. Yes I did change many of my "beliefs" that were based on all the "expert" opinions I'd read for years in books and magazines by well known and respected writers. I, like all of us, accepted them as "fact". As I actually tested what occurs to cast bullets I found many of those assumptions and theories were only based on opinions and guesses at what was happening and were repeated so often by other "experts" and all of us that they became myths and old wife's tales. Frankly I made quite a few enemies on this forum because many self styled experts did not like the truth getting in the way of their own beliefs. I seek the truth and if it proves I am wrong then so be it.

Now to the point here; Do I actually know the answer to the OP's question? No I don't. My own supposition is based on results from other testing that have this far led me to make those suppositions as stated in this thread. Recently I would have said that a GC'd bullet would give more pressure with a given load (all other things being equal) than an identical PB cast bullet. I ran a test on that very question and found there is basically no difference in pressure between the two bullets with the same load. I was wrong and am man enough to admit it and learn. Guess I could have run off to another forum but I've not. So it is with this proposed test. I think I know the answer based on other test results but I have not specifically tested for an answer to the OP's question. If my suppositions are proven incorrect and wrong I will learn from the results and not take any of it as a personal affront.

What if that obturated lubed cast boolit friction surpasses the friction of a unlubed J-word?

My theory on a pressure test comparison of castboolits and j-words:
Light loads will yield results showing J-words creating higher pressures.
Increase the loads to the point that obturation is creating enough friction to surpass that of J-words, then results will start showing castboolits are creating higher pressures.

At what pressure do you think this might occur? In the 44 magnum for a "heavy load" if I load both the 240 gr 44 XTP over the max listed load of 21 gr 2400 and the 429360 (242 gr fully dressed) over the same is that enough pressure? For a lower load I intend on loading both over 8.5 gr Unique. I'm not sure I really want to exceed a published max load for the XTP bullet(?) attempting to find a "point that obturation is creating enough friction to surpass that of J-words" if necessary, do you?

In the 30-30 I was intending on testing a 170 or 150 gr jacketed bullet over a max listed load (probably with H4895) against the same load with a 170 gr 311041 or 150 gr 30-150-FN.

In the 45-70 I was going to use a max load with 400 gr Speer bullets and 400 gr 457483 cast bullet over a max listed TD level load with 4759, a max lever action load with 3031 and a max Ruger #1 level load with RL7.

Any other suggestions?

One great problem of this pressure test, centers on what I have previously stated in this thread [years ago], All things can not be equal, OR BETTER PUT, all "other" things can not be equal.......... One huge issue of "all other things not being equal" is having two projectiles that have the same shape[nose ojive] and same volume and same weight...So when they are seated in the case the same, there will be the same jump to lands (or lack of jump), and same case capacity, so there is a same burn pressure rise. Also the projectiles should be the same diameter, so the case tension is the same.

Those "variables" can easily be adjusted for. Let me say this based on my past experience from other testing indicates unless there is a long free bore to the throat a difference of a few thousandths in bullet jump makes little to no difference in measured psi. What does make a difference in smaller capacity cases is a difference in seating depth (not to be confused with the cartridge OAL). Variations in seating depth in smaller capacity cases (mostly handgun cases) can indeed have a measurable effect on pressure.

My plan in the 44 magnum is to seat both bullets to the same seating depth which will still allow proper crimping. In the rifle cases the bullets will be seated to the crimp groove and properly crimped.

The 44 magnum will be tested in a Contender pistol barrel, the 30-30 in a Contender Carbine barrel and the 45-70 in my Siamese Mauser bolt action rifle.

[Larry Gibson]

BTW; I can push 60,000+ psi in the Siamese Mauser.

[6.5 CM]

Squeeze em' down and they go faster ? That was the theory with the 8x60 Mauser that used .323 Js in .318 bores.

[curioushooter]

I contend that it may be application specific.

I have long used jacketed bullet data to develop cast bullets loads and never really gave it a second thought until I had some pressure signs appear in a 357 mag revolver with under starting loads in 2400 (old data in the Lee Manual). The load manuals are all over with 357 because some go by the mid-90s 35,000 PSI recommendation and others use older hotter max limitation, and some folks (LYMAN) are still working with copper crushers!

In handguns I've loaded cast in 10mm, 44 Mag, 7.62x25, and 32-20 (HIGH PSI Contender loads) and have observed that jacketed seem to make max out with lower charges.

[JonB_in_Glencoe]

Larry,
Thanks for the detailed response. If you do some testing as you have mentioned, I will surely give you whatever support I can when you post about it here.

As to my theory, I have no idea when the friction threshold will be crossed. I do suspect it will happen below Max load data if a soft enough alloy is used.

Lastly, while I hear your words, I just can't picture how the variables can be adjusted for enough, to make all other things the same.

[longbow]

On this line of increased bore friction and obturation...

A few years ago I was doing some informal and not terribly scientific penetration testing for different designs and weights of .44 boolits in my 1894 Marlin. Alloy was basically unknown range scrap which was not quite as hard (subjectively) as COWW. All boolits were cast from this alloy then loaded up.

I started with fairly light boolits and worked up to 300 gr.

During this test I was recovering boolits from end grain fir. This was simply a crude comparison of different designs at max. loads to see what I got. I was surprised to recover a Lyman 429421 that had collapsed in the lube groove almost totally. That is an obvious demonstration that the lead is (or at least can be) yielding under the stress of firing. The 429421 casts undersize for my typical fat bored Marlin (SAAMI spec of 0.431") so could obturate that 0.002" from as cast at 0.429" to groove diameter of 0.431" (measured as best I can to actual of 0.4315") but as Larry says then where does the lead have to go? it is contained by the barrel so if stressed to yield it can only get shorter where it is not supported and that is at the lube groove.

This was a published load but right at max. listing for a jacketed bullet. I got no leading and no sign of pressure... that I saw anyway. So, I have to assume that the boolit did in fact ride on a film of lube since there was no leading and the alloy was too soft for the chamber pressure since there was no sticky brass or flattened primer. That load exceeded that alloys yield strength but there couldn't have been any significant increase in pressure due to bore friction from obturation or I would have had sticky brass, flattened primers or a blow up.

Part of my crude test was to determine if a 300 gr. boolit has more penetration than lighter boolits at higher velocity. Basic question was at what point is case capacity reduced to the point of diminishing returns by boolit weight. My answer is not up to 300 gr. boolits! I didn't go heavier.

I think Larry has definite opinions on what the results of this new test will be and so do I but as Larry says, until the test is done we are basing our opinions on what we think, not what we know or have proved. Doesn't matter which side of the fence you are on, it is just opinion until tested.

I'm looking forward to the results whatever they are as we will all learn something. If I am wrong then I will be corrected and will remember the lesson.

Longbow

[GARD72977]

I have seen some really high pressure from 38spl +p factory loads that seemed to be caused by excessive crimp. I have no idea what the charge would have done with jacketed. The point being you can get high pressure with lead

[swheeler]

I'd like to add:
One huge issue of "all other things not being equal" is having two projectiles that have the same shape[nose ojive] and same volume and same weight...So when they are seated in the case the same, there will be the same jump to lands (or lack of jump), and same case capacity, so there is a same burn pressure rise. Also the projectiles should be the same diameter, so the case tension is the same.

Yes that would make it tough to make "all things being equal" impossible actually I believe. If you take a lead bullet and a jacketed bullet of the same profile and weight the lead bullet will be shorter in length, you may use the same seating depth but jump to lands will be different. Bearing lengths will have to be identical or the test is just more "who shot Tony". If you have two RN bullets for loading the 45 auto, one cast and one jacketed(remember the cast bullet will just about surely be shorter)loaded to the same OAL the jacket bullet will likely be the one with the deepest seating depth because it is longer, that should raise pressure.

[Shiloh]

They used lead and tin based metals called babbitt for pour in place bearings.
For resistance to galling.

Shiloh

[Larry Gibson]

And the list of "alibi's" is growing..........

The problem is "all things" are not equal in what the OP asked. The question was what is the pressure if we substitute a cast bullet of equal weight for a jacketed bullet and "all other things" are equal in the load. The key part was "of equal weight". In a 44 magnum revolver, for instance, I dare say very few here recommend shooting a cast bullet at groove diameter which is usually .429. Nor do hardly any here recommend shooting a .308 sized bullet in .30 caliber rifles. The usual recommendation is to shoot .001 - .003 over groove diameter or to size to the throat diameter. The 44 magnums are most always crimped so a crimp will be used in the crimp groove/canalure. I'll not crimp either the 30-30 as most 30 cal reloads are not crimped. Haven't made up my mind on the 45-70.

Thus I am going to test the bullets the way we use them as I suspect that is what the OP means. As the seating depth in the 44 magnum can be a factor I will endeavor to make that variable as close to the same as I can. I will also test them seated to just the crimp groove irrespective of seating depth. Because it's the way most of us load them the .44 cast bullets will be sized .430, the .30 cals at .311 and the 45-70s at .459.

I think the test loads should reflect the way we actually would load both bullets, not adjust everything for every little nuance we can think of.

I will make "all other things" in the load and in the loading of as equal as we do when loading.

[tazman]

I agree with Larry. We can't exactly match a lead boolit and a jacketed bullet. It is most appropriate if we test things as we normally load them.
That is why I use mixed brass when working up most handgun loads. That is how I use them, so that is how I test them. I undoubtedly get more variation that way, but I also know what I'm working with.

[JBinMN]

I agree as well about the testing as "we would load them". To me, it is the performance as the rounds are loaded & fired in "real life" as they normally would be, rather than a comparison with everything being exactly the same for each one. Since we all are most likely to load them and shoot them that way, than try to match "exactly" in what would not be a "real life" experience or situation.


Looking forward to seeing the test results & Thanks to Mr. Gibson for his efforts.

[longbow]

If we want to get into minutia Larry will never complete the test and we will not get answers. Let's be realistic here. "All else being equal" has limits. Larry has pointed out that for cast boolits most do not size to nominal groove diameter, we cast larger, then size but still at least 0.001" larger than groove. Since that is what most people do that is what should be tested... in my opinion anyway.

Bearing length is likely to be different as well. Do we really care? I don't.

Are factory made jacketed bullets "exactly" the same? No, there are tolerances on all manufactured items. From a given manufacturer they should be very close in diameter (within 10th's of a thou) and profile but are Hornady .30 cal. 170 gr. FP bullets exactly the same as Speer .30 cal. 170 gr. FP bullets? I'd suspect very close in diameter but profile/bearing length, not so much. Let's keep in mind that "close" is a relative term. In guns a 0.001" or 0.002" change in bullet or bore is a large change.

I think Larry started out saying that he'd use equal weight bullets of similar shape and equal seating depth for cast and jacketed bullets so in same brass with same powder charge and same primer we get our comparison results between pressures for cast and jacketed bullets. I think that is the right approach.

Since Larry is doing the test and he has the equipment and experience (certainly more than me) I am content to let him do what he thinks best then learn from the results.

Longbow

[unique]

Let's take my example which is a 357Mag revolver. Peak pressure occurs within the first 1/2" of bullet movement which means before the bullet even enters the bore. My cast lead 160gr are sized .3575 and require a push to clear the cylinder. The speer jacketed 158gr I have measure .3565 and basically are a slightly loose fit but just hang up in cylinder. This is real world, typical for most 357 revolvers, so not hypothetical at all.

When I load the jacketed up with 10.5 gr Bluedot (this is non-canister Bluedot and runs a little hot), the primers are normal flat. When I load the cast lead up with the same load and seating depth, the primers are cratered and show evidence of flowing back thru the firing pin hole. Yes you can read primers visually and learn something about pressure especially when comparing one to another.

Basically, my point is, or maybe better stated, my opinion is, there are few if any hard & fast rules when it comes to ballistics and I do not believe for a moment that someone can run a few tests on a few different calibers and then produce a ballistic axiom.

[JonB_in_Glencoe]

And the list of "alibi's" is growing..........

Alibi's ? ...not me ...not one alibi.
In this case, I just believe All things can't be the same, and have stated so...I stated so 4+ years ago.

When you do your testing and wish to post about it here, I will surely give you whatever support I can.

Thus I am going to test the bullets the way we use them as I suspect that is what the OP means.

I think this is a great plan, and probably the only way a realistic comparison can be done. I hope I can learn something from your results.

[Conditor22]

I am watching with interest.

[303Guy]

Cast boolit riveting could cause undue pressures. Been there, done that. The riveting was into the area in front of the case mouth. It could have been caused by a too soft boolit but I cannot rule out a higher powder charge although that seemed unlikely. I cannot say whether the riveting caused the higher pressure or whether higher pressure caused the riveting.

In the case of 357 magnum revolvers exhibiting higher pressure with cast with higher end loads, I wonder whether it could be due to bump up in or before the forcing cone.

I have recovered boolits that were paper patched that show obturation in front of the patch on the ogive. In this case the patched boolit was being swaged down by the bore, displacing alloy forward while under acceleration forces.

[Larry Gibson]

I have the test rounds loaded. They are in;

357 magnum
44 Magnum
30-30
308W
45-70

There are 280 test rounds loaded in 28 tests. There are 14 loads with jacketed bullets and 14 identical loads with cast bullets. A couple of the cast bullets used weigh a few grains more than the jacketed counterpart but they are all close. A complete description of each load will be in the test result report. I will probably start a new thread with that test result.

That will take 8 - 10 hours of testing given; set up, shooting, target changing, entering data in the computer, barrel cleaning, the usual range interruptions, changing firearms, etc.. I am not sure I will get it all done in one test session. If not then each test of a given load with both jacketed and cast will be conducted back to back to keep the conditions as close to the same as that is the comparison we are looking at; the pressure difference between the same load with jacketed and cast bullets of equal weight.

Next I'll enter all the load data into the Oehler M43's program test format in the laptop (part of the system) I use at the range. I am watching the weather forecasts for a good day and potentially a good day following. I'll report back with the results when the test is complete.

[JBinMN]

Thanks for your update! Looking forward to what results you find!

[OS OK]

I have the test rounds loaded. They are in;

357 magnum
44 Magnum
30-30
308W
45-70

There are 280 test rounds loaded in 28 tests. There are 14 loads with jacketed bullets and 14 identical loads with cast bullets. A couple of the cast bullets used weigh a few grains more than the jacketed counterpart but they are all close. A complete description of each load will be in the test result report. I will probably start a new thread with that test result.

That will take 8 - 10 hours of testing given; set up, shooting, target changing, entering data in the computer, barrel cleaning, the usual range interruptions, changing firearms, etc.. I am not sure I will get it all done in one test session. If not then each test of a given load with both jacketed and cast will be conducted back to back to keep the conditions as close to the same as that is the comparison we are looking at; the pressure difference between the same load with jacketed and cast bullets of equal weight.

Next I'll enter all the load data into the Oehler M43's program test format in the laptop (part of the system) I use at the range. I am watching the weather forecasts for a good day and potentially a good day following. I'll report back with the results when the test is complete.

That's awful nice of you...wish I lived in the area to come over and be your range monkey and help any way I can.