basic (I think) bullet type loading question

[whatwehavehere]

What's the concept behind there being different loads for jacketed and cast bullets in the same weight?

 

[natdscott]

Lead, loaded too fast, becomes unable to withstand the torque imparted by the rifling. It then sheers, leading the bore, and killing accuracy.

I don't like it anymore than you.

 

[whatwehavehere]

That adds up. Thanks

 

[mac45]

Friction

 

[oldpink]

The other side of the coin is that lead bullets have less resistance going down the bore than jacketed bullets do.

 

[whatwehavehere]

So then...
Could one figure any powder charge that's safe for a cast bullet to be safe for a copper jacketed bullet of the same mass?..but not the other way around?

 

[oldpink]

So then...
Could one figure any powder charge that's safe for a cast bullet to be safe for a copper jacketed bullet of the same mass?..but not the other way around?

That's probably true, but (theoretically speaking here) it's possible that you'll need data specific to jacketed bullets for handgun cartridges out of rifle length barrels to ensure that the bullet makes it all the way out of the bore.

 

[Fixer]

More friction from jacketed bullets could lead to an unsafe pressure spike at ignition when dealing with max loads.

 

[noylj]

The test labs work loads up to the max average pressure per SAAMI testing.
It just happens that lead will reach the same pressure/velocity as jacketed at lower charge weights. Then, some manuals actually handicap the lead data by lowering the max average pressure for max loads.
If friction was the only issue, then lead bullets, loaded to the same MAP, should be much faster than jacketed bullets.
Some manuals, I think Lyman does it and several powder company load data on the internet, show the pressure for the max loads and often for the start loads.

 

[noylj]

>That's probably true, but (theoretically speaking here) it's possible that you'll need data specific to jacketed bullets for handgun cartridges out of rifle length barrels to ensure that the bullet makes it all the way out of the bore.

Although that was never found in the whole history of metallic cartridges. Decades ago, one of the magazines decided they wanted to stick a bullet right at the muzzle end. They got 40' of barrel and a .25 Auto. Fired a round and noted where the bullet stopped. Don't remember, but they cut off 1/4 to 1/2 the distance from the muzzle to where the bullet stopped, and the bullet traveled further down the barreatto the muzzle. IF there was enough pressure to get within a foot of the muzzle, the bullet came out of the barrel. I believe they had about 20' of barrel with a .25 Auto and the bullet exited that barrel.
Even the .22 LR is still gaining velocity out of a 20" barrel, although the .22 Win Mag appears to reach peak velocity in a 17" barrel.

 

[whatwehavehere]

Thanks everyone for the useful information.

 

[whatwehavehere]

>That's probably true, but (theoretically speaking here) it's possible that you'll need data specific to jacketed bullets for handgun cartridges out of rifle length barrels to ensure that the bullet makes it all the way out of the bore.

Although that was never found in the whole history of metallic cartridges. Decades ago, one of the magazines decided they wanted to stick a bullet right at the muzzle end. They got 40' of barrel and a .25 Auto. Fired a round and noted where the bullet stopped. Don't remember, but they cut off 1/4 to 1/2 the distance from the muzzle to where the bullet stopped, and the bullet traveled further down the barreatto the muzzle. IF there was enough pressure to get within a foot of the muzzle, the bullet came out of the barrel. I believe they had about 20' of barrel with a .25 Auto and the bullet exited that barrel.
Even the .22 LR is still gaining velocity out of a 20" barrel, although the .22 Win Mag appears to reach peak velocity in a 17" barrel.

This is fascinating since it seems to show how significant an effect the compressed air ahead of the bullet has.