Home Forums Hunting & Shooting Ask The Gunwriters Jacketed vs Lead vs Pressure?

All things being equal, does a jacketed bullet of same weight and caliber generate more pressure than a lead bullet?

I have read that a jacketed bullet is harder to engrave and requires more pressure compared to lead. Does this transfer into "Chamber" pressure?

I have compared plenty of Jacketed bullet data to same weight Lead data and there seems to be no direct correlation between bullet composition, powder charge and pressure. Some data will list more powder with the Lead bullet, some will list less and some will list the same. I am talking about from the same manual or powder distributor's data, not from one manual to the next.

I have also read that jacket bullets can produce less chamber pressure than lead, because a properly sized lead bullet seals off the bore and traps the gasses behind the bullet. A harder jacketed bullet does not seal the bore as well or as completely and gasses can escape past the bullet thus reducing "Chamber" pressure.

Is there even an answer to this question?

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.

Interesting, I would have thought it was the jacketed�.learn something new every day!

Same here, from having to drive bullets out of bores. Just goes to show ya, hadn't considered gas sealing.

I knew that watch out or you'll lose your Poobah card

Found this on another forum, what do ya think?

Lower pressures will be observed with lead bullets. Barrel friction isn't the principle reason. Copper jacket alloy has a higher static coefficient of friction with the brass case neck than a lubricated lead bullet does. Also, copper jacket alloy is substantially harder than lead, and, even though it is just a thin skin over a swaged lead alloy core, it takes more pressure to engrave a jacketed bullet with the rifling than a lead bullet requires. The combination of these factors results in higher start pressure and more powder burned getting a jacketed bullet started onto the rifling. Burning more powder before the bullet moves down the rifled portion of the barrel far enough to expand the volume behind it yields higher pressure. This is true for both rifle and pistol.

Nick

Yup. and your chrono will show that with like weight bullets and powder charges.

Here's somedata from Hodgdon's website:

.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.

I don't know who "Nick on another forum" is, but all he has to do is look at the vast amount of pressure-tested data available today to realize he's FOS.

For ships and giggles, I crunched the numbers for three 240 gr. 44 Magnum bullets. One by Lee and two by Hornady. I used 22.0 gr. of IMR 4227.

The two jacketed bullets were shorter in length.

.678 - Hornady HP (23,700 @ 1547 fps)
.710 - Hornady SWC (24,300 @ 1554 fps)
.735 - Lee cast SWC (26,200 @ 1573 fps)

.735 - Lee cast SWC (25,100 @ 1551 fps)

If you throttle back the velocity of the cast bullet, and bring the it in line with the jacketed bullets, the pressure is a tad higher, but not much. - 800 PSI more than the Hornady SWC and 1400 PSI compared to the jacketed HP.

Of course, this is a computer determined pressure projection. For me, it's not really much of a difference. Although, I grant that there is a little more with the lead.

Edited to add: With these same weight bullets, because the length changes (the lead bullet is longer), there is less internal space for the propellant. With the jacketed bullets, the 4227 occupies less than 100% capacity. For the cast bullet, it becomes a compressed load.

This is what I've always assumed since the jacket is generally harder than lead. Not too old to learn new tricks.

Recently, I did a work up in one of my 9.3x62 Husqvarna rifles using Northman 285 gr plain base cast bullets. They measure .368, and are twice-lubed using Alox.

The velocity was 2236 fps with a half inch square of old cotton towel wad, tamped down over the powder, and slightly compressed COW filler to base of bullet. Group with this load is 2.1 inches at 100 yards.

This bullet penetrated six four-litre jugs of water, and was caught in the seventh. That's over 36" of water and more than half an inch of plastic!



You can see how cleanly the bullet is engraved by the rifling. Note, as well, how near perfect the base of the bullet is. No fusion has taken place at all. The gas seal is quite secure.



Now, the point of all this is that the bullet is getting almost the same velocity as the same weight jacketed bullet USING FIVE GRAINS LESS POWDER. Evidently, the cast bullet load generates higher pressure. Enough that five grains less powder gets the same velocity.

Of course, one huge difference is the COW filler, which the jacketed bullet load did not use.


Interesting stuff,
Ted

If we go back about 150 years, the military determined the need for jacketed bullets was absolute, thanks to the introduction of smokeless powder. Because it launched bullets significantly faster than BP, European military developers knew they had to figure out a way to stop lead smearing. A (rare) tip of the hat should go to Paul Vieille (inventor of smokeless powder - France) and Swiss army officer Eduard Rubin (inventor of the bullet jacket).

What we have to remember is that the military set the standard back then. They did over 90% of the research and experimentation with firearms cartridges. As a result, jacketed bullets were here to stay. It didn't take long for new cartridges and jacketed bullets to find their way over to the civilian world.

Shooters have been reloading for many years with jacketed bullets. As a result, many have forgotten how to load lead. Fewer people have that basic knowledge. Most reloaders are scared that using lead bullets is dangerous, restrictive or too complicated.

Many believe that they will line their bores with lead, accuracy will decline, or both. Some are even scared that their firearms will blow up when the bore becomes clogged up and internal pressures will go through the roof.

Does a gas-checked cast differ greatly from one that isn't?

If one bullet is easier to move down the bore than another, then wouldn't the bullet that is easier to move have a potentially greater velocity at the same pressure?

This is, in part, what fans of molly believe, correct? This is also why equal weight bullets with greatly different bearing surfaces can not use the same max load data.

I thought cast bullets moved through the bore with less friction than jacketed (or at least were far easier to drive down the bore) that therefore they achieved equal velocities with lower powder charges.

My experience with cast bullets is limited to pistol rounds and the 45/70, but it is true that equal powder charges will produce higher velocity with the same weight bullet in those cartridges when comparing cast to jacketed.

Since one can drive a lead bullet down the bore with a mallet and brass rod and cannot readily do the same with a jacketed bullet -I believed the lead bullet must have less friction associated with it. Is this not true?

In long guns, you have to watch the pressure and lead hardness. Gas checks let you push the bullet faster, which means higher pressure, before they start to lead.

A general rule of thumb is 1000 fps max. for lead bullets and 2000 fps max. for GC bullets. You can start playing around with these numbers by varying bullet diameter, hardness and bullet style. Most of the lead that I shoot from my 303s, 30-30s, 45-70s and 44 Magnum is GC.

I use heavier bullets, so I do not have to worry about exceeding a self imposed limit of 2000 fps. Other shooters will tell you that they routinely exceed 2000 fps with their cast loads, but I don't bother.

Thanks - good stuff. Does a g-c cast bullet develop appreciably either more or less pressure with a given charge than does a non-checked one?

To be honest, I don't know. I cannot see there being much difference between the two. It's mostly lead riding the bore for both.

I just did a bunch of shooting with cast .22 caliber bullets designed for gas-checks. The alloy was a bunch of wheelweight metal I melted down and mixed together several years ago.

The bullets were all lubed with Lee Alox, but some were sized to .224" with gas-checks added, some were size without gas-checks, and some were left unsized and averaged .225" in diameter. All were loaded in the same brand of .22 Hornet cases with the same primer and powder charge.

The lowest velocity, by far, was with the gas-checked/sized bullets. The highest was with the unsized bullets, but the sized but not gas-checked bullets were very close.

The best accuracy was with the unsized bullets. They averaged about an inch at 50 yards, versus about 1.5" for the sized bullets, with or without gas-checks.

Another of those infamous examples of one.

Pressure aside, for cast bullet accuracy a somewhat soft bullet unsized with a diameter of groove or slightly (.001) larger diameter usually works pretty well.

I have to wonder about bearing surface, lead bullets are not streamlined so as a generalization I would expect modern spitzer jacketed bullets would have less surface area in contact with the barrel.

Very difficult to compare apples to apples in this hobby.