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

65x54,

That's been my experience as well.

My guess is that a lot of new bullet casters have mediocre luck because they assume all cast bullets must be sized. I cast for several of my rifles and handguns, and in most unsized bullets shoot more accurately. Of course, sometimes I try different lead alloys to see which works best, but in general I prefer doing as little work as possible!

Except that most Lead bullets are equipped with Lube grooves which take away from the actual bearing surface.

There is another consideration I think: Obturation.

Those extra few msec that result from the pressure building and pushing on the bullet before it moves. There's likely more hang time with lead than with a jacketed bullet.

I assume you mean the bullet is spending some time expanding (increasing dia.) instead of moving forward? Get your stop watch out and get back to us on that...


MD, and the trap for new casters seems to be as they lead their barrel they figure they need harder bullets.

How about I get back to you right now about that?

I have a couple of computer programs that plot the time spent in the barrel from ignition to exit. You can go with the powder company info or introduce your own information from a strain gauge.

I believe the higher pressure results from the lead obturating and spending more time in the barrel. The lead is more elastic. That allows the pressure to build slightly, as compared to a jacketed bullet.

I'm sure the surface of a lead bullet also results in more friction than copper or gilding metal.

Steve, it could be on the more barrel time thing. However there is no elasticity to lead. It's going to depend on the burn rate of the powder also as to just how much obturation there will be.

Interesting stuff that has a lot of time spent on it before this conversation.

Yes, lead likely has a higher coefficient of friction. This, and its elastic properties would explain the longer barrel time for the lead.

Lots of variables, lots of ifs and buts.

I've miked jacketed pistol bullets that obturate and quite a few rifle bullets do at rifle pressures.

One is also forewarned that at very low pressures jacketed bullets stick in bores much more easily; at higher pressures beyond a lead alloy holding its shape, the lead certainly will create more pressure and if its leading at that point, its pretty unsafe!

Everything exhibits elastic properties. WRT gun barrels, you have a cylinder upon which which the propellant acts. As the pressure increases, the lead compresses slightly. The time it takes to initiate the pressure, until it is sufficient for the lead to move down the barrel would be the barrel time.

From the time the pressure starts until the lead begins to obturate, would be its modulus of elasticity. This would be different for lead and jackets bullets. And, I suspect, different for jackets made from different materials.

Steve,

Lead isn't elastic, since that means returning to the original shape after stretching or deforming due to applied force. Lead is very malleable, however. As Hawk1 notes, even lead-cored jacketed bullets can deform under pressure.

That "elastic" property is more like a deformation; it takes the shape and doesn't return. The same thing happens when the nose hits something; it deforms by force and pressure.

I mistyped, and will try again.

Lead takes longer to move because it has a higher coefficient of friction. It also a low modulus of elasticity, so it will deform more quickly. (All metals have elastic properties. Lead has a low modulus. Elastic properties include both stretching and compression of a material before deformation.)

Because lead is softer and deforms sooner under pressure, it will take longer to move down the barrel. Like pushing Jell-O through a hose, or poking the Pillsbury dough boy before knocking him over. This slightly longer barrel time will allow a higher build up of pressure.

That's not always true though.

Heat treated lead alloys can exhibit zero obturation while a jacketed bullet can still obturate at the same pressure.


I'm not arguing, I'm just adhering to the concept that there are so many variables that occupy this discussion. The extremes however, are pretty much facts.

When you heat treat though, you are changing the properties of the material.

I think that there may be three or four variables, but not too many. It's out of my area, but I had to deal with engineers, so this sort of conversation was a regular event.

The original question, "Does a jacketed bullet of same weight and caliber generate more pressure than a lead bullet?" was answered. I think that we were exploring the reason explain why. I don't think we'll get to the bottom of it here.

Aren't you changing properties when you alloy too?

And lube, plus the pressure the lube can withstand then the size (and in some cases shape) of the lube groove...the position of the lube groove in relation to the bullet base....

And heat. It increases friction.

This is from Buffalo Bores web site, "...Additionally, hard cast bullets create less friction inside the barrel than jacketed bullets and thus we are able to obtain significant velocity gains at lower pressures, than would be possible with jacketed bullets."

Sundles is a pretty savvy ammunition manufacturer.

I took some time and read through my Lyman 48 and Hornady #7, looking for any information on bullet composition and pressure. Hornady had nothing. Lyman 48 had a small paragraph in their, "Mystery of Pressure" section page 99.

It basically said bullets are not created equal and can have a huge affect on pressure. Length, bearing surface, bullet hardness and composition can all play a role in chamber pressure. Hard (jacketed) bullets can be sensitive to bore diameter and rifling style and cause higher pressure.

It went on to say, Don't assume any rule of thumb to be true, especially this one. Sometimes a "hard" bullet shows lower pressure while the softer bullet shows higher pressure. 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.

I got this from Western powders.

Steve,
Lead bullets are generally longer than jacketed bullets, thus using up more case capacity, which in turn increases pressure. Lead bullets usually take less powder to reach max pressure, but generate more velocity than jacketed bullets.


Don W.
CSR Western Powders
406-234-0422