To crimp or not to crimp

Kirkster · Nov 5, 2020

First time really loading for my AR-15. Do you guys put any crimp on the cases? I generally do not for my bolt guns but do put a tiny bit on for my pistols.

Will be doing 6.5CM for my AR10 next.

85MikeTPI · Nov 5, 2020

No Crimp on my 6.5CM in my AR10

steves1911 · Nov 5, 2020

I dont for any of my ar15s or 10s. Plenty of people do. Some will even tell you it will cause problems if you don't. I experimented when I began reloading and couldn't get as consistent results with crimping and my groups weren't as good with a crimp so I quickly gave up on it. Several thousand rounds now and it's never caused me a problem.

Speed3 · Nov 5, 2020

If you're running .001 neck tension you might have problems, running .004 should be fine

outrider58 · Nov 5, 2020

I never crimp .223/5.56 even if the bullet has a cannelure. I trim cases and load to the cannelure. No crimp.

Kirkster · Nov 5, 2020

Speed3 said:
If you're running .001 neck tension you might have problems, running .004 should be fine

Nope, nothing exotic for this. 3Gun ammo, for when the xm193 runs out...

guzma393 · Nov 6, 2020

I don't crimp any of my loads and if I do, it's just to lightly crimp out the case flare for cast bullets or flush it along the crimp groove for revolvers. For 223/556, i just get them to the cannelure and that holds it plenty along with the neck tension.

Mdphotographer · Nov 9, 2020

I use a Lyman M die so I can use a bullet feeder on my Hornady LnL progressive so I crimp .556 to remove the flare. I always crimp straight wall cases,pistol and .30 carbine. Don't crimp my 7mm STW.

Gordon · Nov 10, 2020

I use a Lee factory crimp

tallen702 · Nov 10, 2020

Gordon said:
I use a Lee factory crimp

Same here. Never had an issue.

whistlersmother · Nov 10, 2020

So, when working up loads, how do I know if I need crimp, other than measuring rounds in the mag after previous one's have been fired?

I assume I load cartridges with same variables except for crimp and measure precision and velocity.

tallen702 · Nov 10, 2020

My understanding is that crimp has more to do with the need for reliability of feeding and durability of the round in auto-loading firearms more than anything else. Yes, the amount of crimp will create variations in things like velocity and pressure, but not enough to be appreciably noticeable unless you're doing some serious precision shooting.

Mostly (again, this is my understanding) the idea is to help prevent bullet setback during the automatic loading process which often puts rearward stress on the projectile and can force it farther into the neck of the case. I've seen non-crimped ammo do this in my FAL and PSL-54C. I've yet to see it happen in my AR, but then again, I always crimp my AR loads and they're crimped from the factory.

Melnic · Nov 10, 2020

What Lee says about FCD
https://leeprecision.com/reloading-dies/rifle-dies/factory-crimp-die/
I have not verified through experimentation but I have read that it helps with consistency when you have variables in the neck tension onto the bullet.
But just like anything else, constancy is key and how you set the FCD can help or harm accuracy.

If my die set has a FCD, I set it for a light crimp

To crimp or not to crimp

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