Bullet setback?

[bucketobolts]

Nubi, here with a simple question. I was reading about problems with bullet setback in .40S&W. Is this when the crimp doesn't retain the bullet in the case, causing the bullet to plunge deeper in the cartridge while it is in the magazine?

Thanks in advance!

[Merlin Orr]

Usually setback occurs when the bullet hits the barrel ramp as is being loaded/pushed into the chamber. Good, well adjusted mags with proper feed lips, a good bullet profile and a proper crimp and you will likely never have to deal with it.

[G-ManBart]

Usually setback occurs when the bullet hits the barrel ramp as is being loaded/pushed into the chamber. Good, well adjusted mags with proper feed lips, a good bullet profile and a proper crimp and you will likely never have to deal with it.

Maybe more proper case resizing than actual crimp, but the idea is pretty much the same. R,

[Duane Thomas]

It's not the crimp that stops the bullet from setting back. It's the fact that the resized casing is smaller than the diameter of the bullet, thus you have an area of metal surrounding and gripping the base of the bullet where the casing touches it that is MUCH larger than the crimp-to-bullet area. Also the fact that the casing under the bullet is narrower forms, in effect, a little cup in which the bullet sits, and it cannot be driven backward beyond that "step" in the metal. Want to screw up that effect? Put too much crimp on the bullet, deform it, and also deform the casing so it bells out under the crimp and is no longer narrower than the bullet.

That's why I say that problems with bullet setback are usually not resizing problems, they're too-much-crimp problems.

[boz1911]

Bullet setback is one of the reasons I always use a U-die. Personally I feel it gives me a cushion of safety even though others do not like the U-die. And Duane is correct, too much crimp will cause all sorts of issues.

[bucketobolts]

Good info, now another question. How do I know if my crimp is correct? I follow the dies' instructions of raising the press to the top of its stroke, running the die in till it contacts the shell holder, then backing it up 3 turns.

BTW, I'm using a Rock Chucker press with Lee and RCBS dies

[TreblePlink]

I use the EGW undersize resizing die and the Lee factory crimp die (just a little crimp), and have had no problems in .40

[ima45dv8]

Good info, now another question. How do I know if my crimp is correct? I follow the dies' instructions of raising the press to the top of its stroke, running the die in till it contacts the shell holder, then backing it up 3 turns.

BTW, I'm using a Rock Chucker press with Lee and RCBS dies

A good rule of thumb is to take the diameter of your bullet, add 2/1,000ths (1 for each side of the case), and set the finished diameter of your rounds for that value. As has been said, crimp isn't to prevent set-back. It just needs to straighten out the case and remove any bell that was introduce for bullet seating. Proper (under-)sizing will take care of set-back.

[G-ManBart]

Good info, now another question. How do I know if my crimp is correct? I follow the dies' instructions of raising the press to the top of its stroke, running the die in till it contacts the shell holder, then backing it up 3 turns.

BTW, I'm using a Rock Chucker press with Lee and RCBS dies

A good rule of thumb is to take the diameter of your bullet, add 2/1,000ths (1 for each side of the case), and set the finished diameter of your rounds for that value. As has been said, crimp isn't to prevent set-back. It just needs to straighten out the case and remove any bell that was introduce for bullet seating. Proper (under-)sizing will take care of set-back.

Don't you mean 2/100ths? For example, .40S&W, .400 + .020, for a crimp of .420".

[ima45dv8]

Thanks for the catch, G-Man!

Yes, 2/100's.