Crimping and Plated Bullets/Cast

keys85 · February 19, 2009, 10:37 PM

Let's limit this to straight walled semi-auto pistol cartridges.

When I load a FMJ, I'll usually mimic a factory load and crimp -.002" to -.003", no more, and no less just to ensure there is no set back.

(Diameter of bullet plus [brass wall thickness x 2] minus .002-.003 = crimp)

The only reason I ask, is because I haven't had very good luck with accuracy loading plated bullets. I've played around with seating depth, charge, crimp, etc. But in general, is -.002" to -.003" crimp in on a plated bullet too much? Would I attain better accuracy putting no crimp at all? (My only fear is getting a set back someday...although unlikely.)

How about crimping with cast loads? Is .002-.003" sufficient?

SL1 · February 20, 2009, 08:35 AM

In straight-walled auto-loader cases, the taper crimp is not the main preventer of set-back. That's case tension on the bullet, plus an underexpanded part of the case below the bullet. I try to match an expander plug length to the seating depth of the bullet I choose such that it expands just to where the bullet base will stop when seated when I am belling the case mouth as much as I want with that plug. This leaves a lip in the case to stop bullet set-back. I don't always do that, just when my testing shows that bullets do creep back when chambering. It usually requires modifying an expanding plug on a lathe to get the right length.

You will probably notice that there is a step in the case diameter when you seat a bullet even after expanding the case beyond that point with an unmodified plug. That is because the plug is designed to leave the case under-sized enough to grip the bullet, and the bullet expands the case more when it is seated. This is often sufficient, but may not be with soft bullets, like swaged lead and copper-plated. You can slightly reduce the diameter of the seating plug to try to get a better grip, but that is not always adequate with soft bullets, because the case swages the bullet some. That is when using a modified expander plug is helpful.

SL1

fineredmist · February 20, 2009, 08:53 AM

Cast and plated bullets will perform poorly if they are crimped too tightly so adjust your die so it takes out the "bell" and no more. Just to make you feel better about no crimp, seat a bullet in a unprimed and powderless case and use a vise to push the bullet back into the case and you will see that it requires a bit of doing. The amount of recoil in a handgun is not sufficient to set a bullet back.

SL1 · February 20, 2009, 07:46 PM

Quote:

The amount of recoil in a handgun is not sufficient to set a bullet back.

Bullet setback in auto-loading pistols is a real issue. And, it does NOT come from recoil bashing the bullets in the magazine, as in high-power rifles. In auto-feeding pistols, it comes from the bullet being banged into the feed ramp during the feed cycle. It is more severe for an auto-feed by firing a cartridge than from hand-cycling the action to feed one from the magazine.

That is why I ALWAYS make dummy cartridges to test for set-back when I start developing an auto-feeder load with a new bullet. I load the dummy in a magazine under a factory round of similar power, hand-cycle the factory ammo into the chamber and fire it to auto-feed the dummy. ONLY when I get the dummy to not set-back more than 0.002" for this test do I load powder and start working-up my load.

It does not take much setback to substantially raise pressure in small, high pressure rounds like the 9 mm and .40 S&W. So, be careful.

SL1

February 19, 2009, 10:37 PM	#1
keys85 Junior member Join Date: September 20, 2008 Posts: 199	Crimping and Plated Bullets/Cast Let's limit this to straight walled semi-auto pistol cartridges. When I load a FMJ, I'll usually mimic a factory load and crimp -.002" to -.003", no more, and no less just to ensure there is no set back. (Diameter of bullet plus [brass wall thickness x 2] minus .002-.003 = crimp) The only reason I ask, is because I haven't had very good luck with accuracy loading plated bullets. I've played around with seating depth, charge, crimp, etc. But in general, is -.002" to -.003" crimp in on a plated bullet too much? Would I attain better accuracy putting no crimp at all? (My only fear is getting a set back someday...although unlikely.) How about crimping with cast loads? Is .002-.003" sufficient?

February 20, 2009, 08:35 AM	#2
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	In straight-walled auto-loader cases, the taper crimp is not the main preventer of set-back. That's case tension on the bullet, plus an underexpanded part of the case below the bullet. I try to match an expander plug length to the seating depth of the bullet I choose such that it expands just to where the bullet base will stop when seated when I am belling the case mouth as much as I want with that plug. This leaves a lip in the case to stop bullet set-back. I don't always do that, just when my testing shows that bullets do creep back when chambering. It usually requires modifying an expanding plug on a lathe to get the right length. You will probably notice that there is a step in the case diameter when you seat a bullet even after expanding the case beyond that point with an unmodified plug. That is because the plug is designed to leave the case under-sized enough to grip the bullet, and the bullet expands the case more when it is seated. This is often sufficient, but may not be with soft bullets, like swaged lead and copper-plated. You can slightly reduce the diameter of the seating plug to try to get a better grip, but that is not always adequate with soft bullets, because the case swages the bullet some. That is when using a modified expander plug is helpful. SL1

February 20, 2009, 08:53 AM	#3
fineredmist Senior Member Join Date: November 2, 2008 Location: Wethersfield, ct Posts: 128	Cast and plated bullets will perform poorly if they are crimped too tightly so adjust your die so it takes out the "bell" and no more. Just to make you feel better about no crimp, seat a bullet in a unprimed and powderless case and use a vise to push the bullet back into the case and you will see that it requires a bit of doing. The amount of recoil in a handgun is not sufficient to set a bullet back.