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FCross7 08-23-2009 02:15 AM

To crimp or not to crimp.
I'm planning on getting into reloading sometime towards the end of the year and have already read through the ABC's of Reloading and am now working on Lyman's Reloading Handbook. I don't remember reading much on it in the ABCs, but Lyman says that ammo rifle ammo meant for a semi-auto should be crimped because the bullet can be seated deeper in the process of cycling. Then it also goes on to talk about how crimping usually reduces accuracy. Just wanted to get some info from some of the veterans. Do you guys find it necessary to crimp ammo meant for semi-autos, and if so have you found it to reduce accuracy by very much? Thanks for any info.


RL357Mag 08-23-2009 02:37 AM

I had a bullet driven back into the powder in my AR-15, so I crimp all of my reloads now, particularly in my .308. I have not noticed any decrease in accuracy attributable to crimping in my AR's. I never used to crimp with my bolt action ammo, but since I have started using the Lee Factory Crimp Die on these rifles also, I do not see a significant decrease in accuracy there either. A decrease in accuracy only occurs because crimp pressure is uneven around the circumference of the neck due to neck concentricity problems. If the neck is not concentric with the center axis of the case and die, crimping pressure will be unevenly applied around the neck, causing the bullet to unevenly break free of the neck when pressure overcomes neck tension and the bullet departs from the case. This effect would be insignificant if you seat a bullet out far enough where it contacts the rifling upon chambering. But since all factory ammo is manufactured according to strict COL standards, this allows a bit of leade before the bullet engages the rifling, and non-concentric necks can equate to accuracy problems. This is why they make a tool to measure neck concentricity, as well as a tool to "true" the necks. But these are mainly tools used by bench rest competitors and manufacturers of match grade ammo. For the average shooter, crimping is a good thing and can avert safety issues caused by bullets becoming dislodged.

FCross7 08-24-2009 01:14 PM

Once again, thanks for the info. that answered my question. And from the sounds of it, your way farther into reloading than I plan on being for a while. Sounds like you've been doing it for a year or two.


1hole 08-24-2009 01:21 PM

Crimp or not? Why not make it simple. When you start, load half a box with crimps, other half without. See which works best. Your own experience using your own equipment will be much more helpful than anything we can tell you.

FCross7 08-24-2009 01:27 PM

I thought about that. But then I thought, what if when one of the non-crimps cycles, the bullet gets pushed back into the powder and the thing blows up in my face? Doesn't sound like too much fun.


RL357Mag 08-24-2009 10:23 PM


Originally Posted by FCross7 (Post 149777)
I thought about that. But then I thought, what if when one of the non-crimps cycles, the bullet gets pushed back into the powder and the thing blows up in my face? Doesn't sound like too much fun.


In an AR-15, and definately in the LR308, it's not a question of "if", it's more a question of "when". If you really want a comprehensive book on reloading which includes range ballistics of all commercially available loads as well as definitions and theory, pick up a Sierra Reloading Manual. It contains very helpful information for range use such as bullet drop, velocity, energy, max. point blank range, etc. from 50 yds. to 1000 yds. It also contains load data for hunting and accuracy. It's one book you will keep going back to over the years. It offers step by step reloading instructions and tells you "why". It's in binder format and I can't tell you how many times over the last 15 years I've removed and copied pages to take to the range for specific bullets I reloaded.

robocop10mm 08-25-2009 02:36 PM

As long as you are not pushing the upper limits in your loads, a small amount of bullet set back should not cause the gun to "blow up in your face". If the bullet was severly set back in a bottleneck case, it would be pushed beyond the neck and would allow some powder to leak. This would also allow the excess powder to burn ahead of the bullet or perhaps not burn at all thus theoretically negating the reduced volume caused by the set back.

Depending on the gun/magazine combination, there may or may not bee a need to crimp. I prefer to crimp because of the possibility of the ammo being used in a SHTF situation and my life may depend on even my target ammo.

For cannelured bullets I crimp sufficiently to have the mouth visibly into the cannelure. For non-cannelured bullets, I crimp very lightly, just noticible to try to attain a balance of bullet hold vs. jacket integrity.

cpttango30 08-25-2009 02:59 PM

If you buy Hornady or RCBS dies they both roll crimp unless you set them not to.

For an AR or other semiauto I would crimp just to be on the safe side.

FCross7 08-25-2009 03:09 PM

Ok, thanks for all the info guys. I was more than likely gonna crimp anyway just to be on the safe side but I just wanted to see what everyone thought.


Silvertip 44 09-02-2009 01:36 AM

I have not crimped ammo for .30-06 or .308 in years. I have loaded for a Remington 742 since about 1975 and have not crimped. Now i load for four M1 Garands, three M1As and an AR 15 and still do not crimp.
I did switch from Hornady 150 gr fmj bullets (cannelured) to Hornady AMax 168, Sierra MK 168 and Nosler BT 168 with no cannelure.
I was informed a while back by an old retired army armorer that my M1 and M1A would more accurate with the non cannelured bullets. I think he knew what he was talking about.

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