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

[RobS]

And it may be useful to note that those Cast Perf boolits are typically harder than
the hinges of hades, so likely on the high end of boolit pressures.

Bill

Very possibly wrong, they could result in less pressure with higher pressure situations vs a softer boolit.

[Whitespider]

Very possibly wrong, they could result in less pressure...

That's what I've seen, using non-scientific observation as evidence... softer tends to run at higher pressure, and more often higher velocities. I actually ran an unintentional data-collecting comparison of soft vs. hard(er) one time.

When I got my .38-40 Blackhawk I was anxious to shoot it and picked up some Hornady soft-swaged 180 grain SWC's, a week later I bought some hard-cast 180's at a gun show. I'd been shooting the Hornadys with 17.5 grains of Accurate 5744, so I loaded some of the hard-cast with the same charge. I set up my chronogragh using the Hornadys and saw around 1200 fps, primers slightly flattened and zero barrel leading. When I switched to the hard-cast I saw only 1040 FPS, no primer flattening and they leaded the bore... I ended up increasing the hard-cast charge to 19.0 grains, giving me 1150 FPS, slightly flattened primers and barrel leading was near eliminated. Just going on my amateur ballistition observations... the hard-cast required more powder to achieve like pressure, yet still appeared to give lower velocity (shrug).

By-the-way, those hard-cast actually weighed closer to 175 grains (like 177 and the Hornadys a true 180) and measured .4013-.4015 and my Blackhawk barrel slugs .4008, cylinder mouths .4014.
*

[RobS]

Whitespider:

Yeah another part about commercial hard cast that even when sized appropriate there may be leading until pressures increase can often be caused by the crayon lubes used for ease of shipping. A good, quality, soft lube helps negate possible leading due to being of a tougher/harder BHN because if flows more readily from the start of the boolit's journey. Some people have also taken hard cast that come with this crayon lube and have hand dipped with tumble lube to add another layer of lube protection if you will to make up for the less "flow-able" commercial lube.

[RobS]

When I got my .38-40 Blackhawk I was anxious to shoot it and picked up some Hornady soft-swaged 180 grain SWC's, a week later I bought some hard-cast 180's at a gun show. I'd been shooting the Hornadys with 17.5 grains of Accurate 5744, so I loaded some of the hard-cast with the same charge. I set up my chronogragh using the Hornadys and saw around 1200 fps, primers slightly flattened and zero barrel leading. When I switched to the hard-cast I saw only 1040 FPS, no primer flattening and they leaded the bore... I ended up increasing the hard-cast charge to 19.0 grains, giving me 1150 FPS, slightly flattened primers and barrel leading was near eliminated. Just going on my amateur ballistition observations... the hard-cast required more powder to achieve like pressure, yet still appeared to give lower velocity (shrug).
*

This has to do with pressures that are being placed on the cast boolits. As the expanding gasses from the powder being ignited take form there is force or pressure on the base of the boolit and the cylinder throats/forcing cone/bore (in your specific case) then applies force to the front of the boolit. The force on the base of the boolit combined with the force on the nose of the boolit applies pressure on the boolit itself causing it to compress and push outward on the cylinder throat/forcing cone/bore. A softer boolit can be subject or is capable of being compressed to a greater extend vs one that is harder should a powder charge be the same creating more outward pressure exerted to the bearing surfaces of the firearm. Associated then with a softer projectile in your scenario it resulted in a higher chamber pressure which translated to higher velocities as said force compressed the boolit to a point of creating more pressure on the bearing surfaces of your firearm.

[MtGun44]

Hmm. Seems backwards to me. Most boolits are oversized and must be sized down as they enter the
bbl, so harder would take more force to size down.

Bill

[RobS]

Hmm. Seems backwards to me. Most boolits are oversized and must be sized down as they enter the
bbl, so harder would take more force to size down.

Bill

Not necessarily......think about this particular thread in question. Why do labs have data that shows lower pressure rounds such as 45 auto, 38 special etc. that use swaged boolits using powder charges that are equal to jacketed yet the swaged boolit yields more pressure/velocity vs the jacketed. Or some rifle data shooting jacketed with less pressure vs cast boolits with similar weight between the two projectiles and the same powder charges. Then the opposite with the example I pulled from the hodgdon site and posted in this thread.

Considering different hardness levels between cast boolits, the answer lies in what pressures are placed on the cast boolit itself and how hard the boolit is and how much force is placed on the boolit to push it through the throats/forcing cone/bore in revolvers or just the throat/bore in closed chamber systems. It's all relative to each particular situation i.e. load powder charge/primer, boolit (BHN) or bullet (jacketed projectile), firearm in used during testing and the testing equipment...............that is why reload data has both accounts as labs have tested it..........as I said it's all there in each labs data.

[Whitespider]

Seems backwards to me. Most boolits are oversized and must be sized down as they enter the bbl, so harder would take more force to size down.

You're assuming that peak pressure is developed as the boolit enters the rifling and is being "sized" down. Under some certain conditions that may possibly be true... but likely it ain't for the majority. It takes time for powder (modern smokeless powder) to burn and reach peak pressure, usually at some point after the boolit/bullet has entered the barrel. That's the main purpose of different powder burning rates, matching that rate to the variables of projectile weight, construction, friction coefficient, desired velocity, barrel length, expansion ratio of the cartridge and some others more technical and/or obscure.

Remember that we're only talkin' 'bout peak pressure here in this thread...

Look at it this way...
Except for some rather minuscule differences between single and double base powders... 10 grains of Bullseye contains the same amount of energy as 10 grains of IMR7828, the difference is in how fast it releases that energy (and it should be noted that the rate of release may/can/will change from cartridge to cartridge, or even with different boolits/bullets within the same cartridge).
*

[MT Chambers]

Maybe this explains why AA powders never make it on to the store shelf??

[Quiettime]

When I first got a .45 Colt revolver, I did not have any cast bullets in my stock. All I had .45 cal was some FMJ 230 Winchester bullets. I made some loads using data for 255 gr cast (lighter bullet, should be safe right?) using Universal Clays powder. OAL was adjusted by eye, based on the beginning of the ogive placed just ahead of the mouth of the case. Went to the range. Piff piff! Recoil was mild to say the least. You could almost see the bullets going downrange and they were not penetrating a piece of 5/8 plywood from 25 yards.

What is interesting is there was a LOT of unburned powder particles in the gun and left in the cases...

Did the jacketed bullet slow the load down because it is harder to deform?

Did the lighter weight bullet not create enough resistance to raise the pressure enough to burn the powder?

Did the different seating depth not create enough pressure?

Did the different bearing surface have an effect?

I'm with Whitespider, I think there are too many factors involved to definitively say this or that. You can take two molds, one smooth sided and one with a lot of lube grooves both the same weight and have totally different bearing surfaces. Hollow base, bevel base, plain base...Does the chamber have a lot of freebore, a sharp leade angle, compound leade etc etc etc

One thing I learned for sure that day is you cannot substitute lead data for jacketed data or vice versa!

[JonB_in_Glencoe]

Quiettime,
I'm not sure if your questions are rhetorical? or if you are truly looking for an answer?
First, some older 45 colts have larger specs...like .454" you could have some issues with severely undersized bullets and lots of blowby.
Second, light loads of "shotgun" powder in pistols are notoriously dirty, because those powders are designed to burn clean at a certain pressure, anything less you get an incomplete burn.

[Whitespider]

...light loads of "shotgun" powder in pistols are notoriously dirty, because those powders are designed to burn clean at a certain pressure, anything less you get an incomplete burn.

That has problems flying in my world.
Most shot-shell loads run in the 7500 to 10,500 PSI range... even starting loads for the .45 Colt meet that criteria.
The Hodgdon website doesn't list 255 grain cast or 230 grain jacketed... but they do list 250 grain cast and 225 grain jacketed.
Interestingly the Universal Clays starting load for the 225 grain jacketed is .1 less than for the 250 grain cast (6.4 vs. 6.5).
I don't know where Quiettime got his data, or what powder charge he used... but, going on Hodgdon's web data, it should have been close enough for shooting dirt clods.
*

[JonB_in_Glencoe]

That has problems flying in my world.
Most shot-shell loads run in the 7500 to 10,500 PSI range... even starting loads for the .45 Colt meet that criteria.
...snip

A quick look in my Lyman manual had a starting load of Clays for 255gr. cast in 45 colt developing 8700 CUP. Then put a lighter weight undersized J-word in there and maybe the pressure could be less than 5K ? Just a guess.
Quiettime listed no details, so it's hard to guess, I was trying to help him out.
Jon

[singleshot]

The energy of activation and first few ms of burn are critical. A shotgun is designed to have zero blow-by during the critical ignition and initial pressure build phase. In fact, there is virtually none until the gas seal exits the shell. In a 45 LC, if that initial ignition and pressure build is lost (probably due to an oversized chamber in addition to the oversized bore) there simply won't be enough energy of activation to get a decent burn.

And velocity is not about peak pressure, it's about the area under the curve, so to speak.

[303Guy]

You're assuming that peak pressure is developed as the boolit enters the rifling and is being "sized" down.

Bingo! And therein lies the answer.

There still remains gas leakage with jacketed's which would surely reduce peak pressure. Someone once embarked a project to turn a 270 Winchester into a magnum and to achieve that end he had his custom barrel cut with extra deep grooves to allow gas leakage. He claimed to achieve higher velocity with heavier charges by doing this, relying on leakage to keep peak pressure within allowable limits. He used more of a slower powder.

[Larry Gibson]

And velocity is not about peak pressure, it's about the area under the curve, so to speak.

That is correct.

If you saw time/pressure curves of low end target/SASS loads you see just how uneven and erratic powders burn, even the fastest of them.

Larry Gibson

[sawzall]

Better check your facts.
Typically the babbitt material covering main and rod bearings contains less than ½% lead (like o.3 or o.4%).
They are a tin based alloy and contain more copper and/or antimony than lead. They work because of a "pressurized" lubricating system that "floats" the crank journals within them. The reason for the "soft(ish)" layered alloys is not for their "slipperiness"... rather so it doesn't destroy the crank when the bearing fails.

The soft coating on bearings is for "embedibility" or the ability to capture small particles and allow them to be driven into the bearing instead of the crankshaft / camshaft.

[303Guy]

The soft coating on bearings is for "embedibility" or the ability to capture small particles and allow them to be driven into the bearing instead of the crankshaft / camshaft.

Is that correct? "Embedibility" sounds like small particles will get embedded and abrade the journals. I'd have thought the material used has a high fluid friction so as to trap the oil film and force dynamic lubrication.

[sawzall]

Is that correct? "Embedibility" sounds like small particles will get embedded and abrade the journals. I'd have thought the material used has a high fluid friction so as to trap the oil film and force dynamic lubrication.

If the bearing surface is too hard, the particles will flow between the surfaces and abrade both. The soft layer of "babbit" type material allows the particles to be driven down low enough to be covered by the hydrodynamic wedge of oil that lubricates the bearings and journals. We are talking tiny, almost microscopic particulate matter here though. Bigger pieces will still get embedded into the bearings but will exceed the film thickness of the oil and score the crank or cam journals. Bearings have 3 layers to them. The steel backing, or shell, gives them strength. A layer of a copper alloy gives them "conformability" which allows the bearing to kind of adapt to imperfections in the bearing journal and the final, very thin layer of the babbit (not actually babbit anymore) for the embedability described above. It's a fine line for bearing manufacturers to build bearings that offer good protection and last a reasonable amount of time. And an engine bearing should really never in it's service be run "metal to metal" as stated by another poster in this thread. When they are run dry in such a fashion, catastrophic failure results. They are lubed with assembly lube on initial assembly and then generally prelubed with oil pressure before first start up. Then, when the engine is shut off, a very small amount of oil stays between the surfaces giving initial protection on start up which really is a very light load on the engine. They start pumping oil as soon as the engine begins turning over and build oil pressure. A gauge doesn't always reflect this. It does take a little bit of time for the oil to form the hydrodynamic wedge that actually protects the surfaces when running which is why you should never rev an engine high right as you start it. This is when most normal bearing wear occurs, unless there are other problems with the engine.

[BAGTIC]

Similar to gasoline where low octane gas actually contains more energy than high octane gas. The advantage of high octane is that it can be used at higher compression (pressure) levels before it begins pinging (detonating). Higher pressure levels permit more power to be developed within the same engine displacement (case capacity).

[TXGunNut]

I think the engine bearing material is porous so as to hold oil in the pores, otherwise, you would wipe out a crank evertime you started the engine.

Ummm...No. But let's not get any more off-topic here.