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

[WallyM3]

Are we talking static or kinetic coefficients of friction?

[JonB_in_Glencoe]

I didn't say "all things", I said "all else".
In other words, the same bullet will gain velocity if pressure is increased (by increasing the powder charge)... but the same can't be said if two different bullets are used. You can't expect two bullets of same weight but different construction (construction may mean material, shape, bearing surface, or any number of other things) to achieve identical velocities just because pressure is identical... one or the other is likely to go considerably faster.

Pressure is only relative to the same bullet... not two different bullets.

I was referring to the OP

[rking22]

Rereading that posting several times , all things are not equal ! We "hardly ever" shoot an unlubricated lead bullet and we "hardly ever" shoot a lubricated J word. Also a cast bullet with those loob groves or TL rings has signifigantly less bearing surface than a same weight copper clad bullet. The force required to engrave the rifling is reater with the jacketed due to this bearing surface difference as well as a generally "harder" jacket to deform. This all happening just as the bullet starts to move. Case volume determined by seating depth makes it near impossiable to compare from load data in manuals without measuring the compared bullet lengths . Oh well , I agree, more lead for us is a good thing. Scare em all away!

[MtGun44]

The journal bearing has two modes - as the engine just starts you have sliding friction as the bearing
surface is directly in contact with the steel journal, with a bit of oil. As the speed builds up, the oil
film is pumped in and the bearing actually lifts off the surface on a few thousandths of oil film and
never again touches the journal until shutdown as the rotational speed drops below the liftoff speed.
Zero wear when running, only at startup and shutdown.

Boolits are like the bearing prior to liftoff - metal to metal lubricated contact, but not static.

Bill

[hermans]

I would like to get a little more than a shake of the head from Gear....this is what makes this the best forum ever!!! Keep it up guys!!!

[Whitespider]

I was referring to the OP

Oh... my bad for jumping on it... my apologies.

[beagle]

Interesting thread but bunk IMO. We are assuming everything is equal here. Now, a jacketed and cast bullet will never be the same. We might try to get them identical but it can't be done. Another variable we're not considering is the diameter. Ever try shooting a .308" diameter cast bullet in a .30/30? I'm betting the jacketed will have a higher pressure with the excess freebore by shooting an "undersize" (to us cast shooters who normally use .310s or .311s) cast bullet. We'll also probably have bad accuracy and leading as a bonus plus less velocity./beagle

[mold maker]

Another NONE equal exist in the grip of the brass crimp on the soft lead (with lube), and the harder surface of jacketed.
The pressure needed to break the bond is less with cast. Thus the movement of the boolit is sooner, increasing the gas pressure space, and giving the boolit a head start.
If the boolit is soft enough to obdurate it does so as it clears the case mouth sealing it's self to the throat.
The case with jacketed is a tightener bond with the jacket and the case, and a slower initial movement, meaning higher pressure to begin with.
I know this just muddies the water, but has to be addressed in the total discussion.

[WallyM3]

"Boolits are like the bearing prior to liftoff - metal to metal lubricated contact, but not static.

Bill"

This is what I was envisioning for lubed lead. In the case of copper jackets, the coefficient would initially be considered static (against brass), then dynamic (against steel).

The effects of the different lubrication might be slightly different, but probably way too small to influence calc. of µ.

Too many variables to contemplate in building a model that might produce meaningful result. Still, it's fun generalizing.

I worked with 4 bearings that were 18.25" in diameter. We had to artificially begin their rotation well ahead of being turned by the prime mover (35,000 hp steam turbine) in order to ensure that there was an oil film between the steel and the babbitt metal (in one bearing's case, lignum vitae and water).

[Marlin Junky]

...Yes, they do. It all comes down to the frictional co-efficient. Gilding metals like copper slide more readily than lead does on a steel surface. You can write your name on a piece of paper using a lead bullet much more readily than you can with a copper one. This tendency to smear, which is why it leaves a track on paper is also why it tends to grab the barrel more quickly and increase pressures. Using jacketed bullet data with a lead bullet of the same weight will result in higher pressures, everything else being equal.

That is one of the most pathetic explanations I've ever heard... problem is, lots of beginners will believe it.

The real answer lies in real physics.

Obturate a soft bullet (boolit) to the point where you have excessive force vectors normal to the axis of the bore vs. parallel to the axis of the bore and pressure behind the "obstruction" (the boolit) will escalate.

MJ

P.S. it has nothing to do with the coefficient of friction of Pb vs. Cu as given enough obturation of either material, their "COF's" will skyrocket to the point of becoming obstructions... BOOM!

[Digital Dan]

I have to smile a wee bit about this thread. There was just recently a similar thread at 24hr Campfire espousing what the OP in this thread said. It was largely supported by the jacketed bullet crowd in all the same fashion, load book and Oehler PBL reference, etc. etc.

If you all want to put a symposium together to debate this I'll bring the popcorn.

[BAGTIC]

All things CAN'T be equal !

It's kinda like saying this...All things being equal, If a ship and a train have the same size engine, A train can haul more freight than a Ship, because the water creates more friction against the steel hull of the ship, than the train's steel wheels on steel rails.

NO WAY. Ship can always haul more with same horsepower. For one thing ships always work on the level and don't need extra h.p. for hill climbing. Trains haul it faster but at the speed ranges where most ships operate trains can not come anyways near the ton/miles performance of a ship.

[JonB_in_Glencoe]

Bagtic,
I'm glad you agree with me that "all things can't be equal"

[BAGTIC]

Whether a cast produces higher or lower velocities can vary according to particular powder charge can depend on the particular bullet weight and resistance. If given bullet weight is combined with a powder a little to slow to be optimal a higher resistance bullet is can raise pressures and combustion efficiencies thereby increasing velocity. If a max load using a resistance bullet has a lower resistance bullet substituted the lower pressures generated will produce lower velocities until the powder change is increased to increase pressure.

Even if the bullet seating depth is the same it does not mean that travel distance to contact with the lands will be the same due to different bullet OAL and ogive shapes.

Also a softer bullet may expand more in the throat and the need to be swaged down more at the leade while a harder bullet may expand little.

Military tests have showed that military FMJ .308 bullets using dead soft lead cores raised pressures compared to the same bullet with harder lead cores due to the softer cores actually expanding bullet diameter due to high chamber pressures.

There is no single solution or explanation.

[gtgeorge]

Wow what an interesting debate. I can only see this being settled for sure with someone with pressure testing equipment since so many ways to look at things. One can look at how hard it is to push two same weight bullets with equal bearing surface through the bore but then have to wonder how that compares to under pressure with how the bullet may swell, the heat involved and what happens with the lube etc. when being fired. It would require finding 2 bullets of the same weight, bearing surface and seated to the same depth in identical case volumes and a pressure measurement taken.

Since without all this being available I will also add my WAQ to this in that I believe the lead develops more pressure since I think it seals the combustion chambers better from start to finish. I do think it will move easier down the bore as it progresses due to the lube coming into play but do not know how pressures actually build. Isn't the highest pressure very early on in the combustion process?

But then on the other hand when I compare loads I have worked up in a 400 CB with similar weight lead and copper, I am able to add more powder and get more velocity before showing pressure signs on hot loads with lead. Once again a non scientific guess.

It would be really nice if someone with test equipment could and would do some side by side testing to determine the true answer. I wonder if Western powders did indeed base that info on actually testing taking into consideration all the aspects involved?

[Whitespider]

There is no single solution or explanation.

And that there says it all‼

[Super Sneaky Steve]

Some other factors to think about.

Our cast boolits are often a little over sized. If an oversized jacketed bullet were used what would that do to pressure?

Second, after whacking thousands of jacketed boolits with a hammer I can say they aren't all the same hardness. Both jacketed and cast boolits have different degrees of hardness. Comparing a very hard cast boolit to a soft jacketed boolit doesn't seem fair. I'd like to see a test where the cast boolit is the same hardness as the core of the jacketed boolit.

[steve4102]

All things being equal a Lead bullet will generate HIGHER pressure that a Jacketd Bullet with identical powder charges.

Western Powders is not the only ones who have published this.

Lyman 48 page 99 says,
A soft bullet may cause higher pressure because the bullet is so malleable that the sides will push hard against the bore when high pressure is exerted on the base.

Handloader Magazine says,
Normally a lead bullet of the correct diameter and hardness produces more pressure with the same powder charge, because it does seal the bore better.

Hodgdon's web site,

.44 Magnum handgun--
240 cast/ 22.0 IMR4227/ 33,300 CUP
240 jacketed/ 22.0 IMR4227/ 28,400 CUP

.38-55 rifle--
250 cast/ 27.0 H322/ 27,000 CUP
255 jacketed/ 27.0 H322/ 25,500 CUP

250 cast/ 24.0 IMR498/ 36,200 CUP
255 jacketed/ 24.0 IMR4198/ 31,400 CUP

Please not that even though the jacketed bullet in the .38-55 weighs 5 grains more, pressures are less with the same powders charges. And in all the above instances, the STARTING load with jacketed bullets is the MAX load with cast bullets.

Take a look at Hornady #7 45 ACP data for example.

230gr FMJ COL = 1.230. This bullet measures .651 inches.

230gr Lead RN = 1.245. This bullet measures .640 inches.

So the Jacketed bullet is .011 longer and is seated .015 deeper, for a total of .026 deeper.

Data.
N-340 Lead, Max = 6.6gr. Jacketed. Max = 6.7gr.
Even with the .026 deeper the jacked bullet used more powder.

Clays Lead, Max = 6.2gr. Jacketed. Max = 6.4gr
Even with the .026 deeper the jacketed used more powder.

231 Lead, Max = 6.2gr. Jacketed. Max = 5.7gr
Here the Lead bullet with less seating depth used more powder. Maybe due to COL, maybe due to the lead bullet.

Unique Lead, Max = 6.3gr. Jacketed. Max = 6.1gr
Again we have more powder with lead than we do with Jacketed.

We can also look at Speer #13. They list their 230gr L-RN at 1.270 COL and their Jacketed 230gr TMJ at 1.260. I do not have the length of the L-RN compared to the TMJ, but of the five(5) powders that are used for both the Lead bullet used significantly less powder than the Jacketed TMJ.

All we have to go on as handloader is load data. Theories are great and often times helpful, but when they conflict with actual pressure tested data, it's best to follow the data and no the "Theory".

So far I have seen no evidence here that Lead bullets build less pressure than jacketed.

[RPRNY]

I am firmly in the all other things being equal, a jacketed bullet will deliver high pressures than a lead bullet camp but am prepared to listen.

If boolit pressures are higher, why are faster powders generally used for the same weight cast vs jacketed? Is this only to achieve the lower velocities that cast favor or because less resistance requires a faster powder?

[Uncle R.]

Veral says cast boolits give less pressure.
My experience agrees with Veral but I can only judge pressure from things like primer appearance, case head appearance and case expansion. Obviously I can get no closer than a SWAG but keeping in mind the less than certain nature of my results I'll still say my experience agrees with Veral.
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There is a proviso that I've very seldom used extremely soft boolits - in fact for many years before I found this place I used boolits that were harder than optimum. Those hard boolits almost always gave higher velocity than jacketed (verified by chronograph) with equal charges, and if there was a pressure difference large enough to note by my SWAG methods the boolits gave less pressure. For many years and in dozens of different loads I have routinely swapped my linotype hard gas-checked boolits in magnum handgun jacketed recipes and never had a problem.
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Just my experience. Even so I wouldn't be too surprised to see very soft boolits or heavily leaded bores give higher pressures than jacketed.
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Uncle R.