Crimp job for AR10's

[Rando_Kommando]

I have a question about how much of a crimp is needed for a Semi Auto like a AR-10. I made a fresh batch of 308 168g Hornady ELD match, I put a small crimp on the neck after research showed that semi auto's with strong actions like a AR-10 need a good crimp.

I did a test and the OAL length before was 2800" before chambering and afterwards it seems to have expanded to 2803. Just wondering if I should use a stronger crimp or not worry about it and shoot.

 

[LVLAaron]

Frankly I wouldn't worry about 3 thou on an auto-loader. If you were building a true battle rifle I'd get cannelure bullets and crimp'em hard.

 

[Rando_Kommando]

Frankly I wouldn't worry about 3 thou on an auto-loader. If you were building a true battle rifle I'd get cannelure bullets and crimp'em hard.

Got it. I shoulda have provided more context. It's a 20" barrel length setup as a DMR bench gun with a 5x25 PST FFP scope. Trying to squeeze as much accuracy as I can. But your right maybe 3 thousands isn't much to worry about.

 

[LVLAaron]

My two cents... As long as it's consistent, it shoots, and doesn't cause any problems, continue on.

 

[Scott-ak]

I shoot a 22" AR and load w/ELDMs. I don't know how you measure crimp. I've never seen a round grow but have had a few shrink. I started with a light crimp. It was very concerning to be shooting loads at 2600 fps and have a couple go 3200. I tightened the crimp until it stopped.

 

[Ray123]

Shot many AR 10 & 15 rds with no crimp... same stuff shot in a bolt gun. But when I use a crimp it's a light to moderate in a separate station with usually a lee factory crimp die...and not necessarily on the cannelure and most bullets I use do not have one. Push down fairly hard on the bullet point of a freshly loaded cartridge on the reloading table ... if the measurements of the COAL are the same, before and after ...that's usually sufficient to hold the round in the mag and during cycling. Correct neck tension usually does the job...and a light crimp to aid in feeding... kinda like a 9mm Luger, for a visual...but also works on the 308, the 50BMG and a host of others...works for me...I'm definitely not a heavy crimper. And I do measure the crimp on 9mm, 45 acp, and 380 with a caliper...don't want them over crimped, because the head space off the case mouth.

 

[lb-ft]

+2 on the Lee Factory Crimp Die. They’re fantastic.

 

[divingin]

Got it. I shoulda have provided more context. It's a 20" barrel length setup as a DMR bench gun with a 5x25 PST FFP scope. Trying to squeeze as much accuracy as I can. But your right maybe 3 thousands isn't much to worry about.

I'm with Aaron.

I suspect that, assuming you're loading to mag length, you'll be jumping the load a lot. Especially with the more streamlined (long nose) bullets. I don't think that a few thou added onto the 20-50 (or more) thousandths from fitting the mag is going to affect much. You'll probably get more improvement by choosing a jump-tolerant bullet (SMK's seem to be; I'm sure there are others.)

As an aside, I just went through this with a friend of mine. Cherry-picking barrels and chambers to try and get a short throat on his AR-10 so he could run VLD's. Didn't work, as far as I know. It did put me over my text message limit a couple of months in a row though (a limit that I no longer have.)

 

[Doug Casner]

I crimp for all my autos rifle or pistol. 223, 300win. mag,9mm ,45 acp. Dont know how to measure it. Just crimp them till they feed good and lock er down. Doug

 

[Catfur]

I shoot a 22" AR and load w/ELDMs. I don't know how you measure crimp. I've never seen a round grow but have had a few shrink. I started with a light crimp. It was very concerning to be shooting loads at 2600 fps and have a couple go 3200. I tightened the crimp until it stopped.

That does not compute. To get that the bullet would have to be shoved ludicrously far down into the case for that to happen, like so just the tip was showing.

 

[whatsupdoc]

Check the case shoulder before chambering and after chambering, You may find your large
frame gas gun bumps your shoulder a bit.

By crimping without canalure you may be distorting the bullet jacket and there is no way to
judge how much crimp is required.

 

[Scott-ak]

That does not compute. To get that the bullet would have to be shoved ludicrously far down into the case for that to happen, like so just the tip was showing.

you are correct. I just ran it thru GRT. So what do you think, an occasional chrono problem? Odd that it has never happened since I started crimping

 

[Rando_Kommando]

Check the case shoulder before chambering and after chambering, You may find your large
frame gas gun bumps your shoulder a bit.

By crimping without canalure you may be distorting the bullet jacket and there is no way to
judge how much crimp is required.

I believe this to be true. The action on this AR-10 is pretty violent, it just slams them into battery. It's up there with my M-1 Garand. I was thinking the same thing about the shoulder being pushed back. Granted I haven't used a OAL gauge to find my lands, I'm just using the data from my Hornady app which states 2800 is ideal for COAL

 

[Twdmar]

You can test your crimp by pulling a bullet to see if the crimp is cutting into the jacket on a non cannellured bullet. Most bullets do fine with a light crimp, though if you want a lot of crimp, the cannelure is necessary. As someone mentioned above, enough neck tension should probably work without a crimp.
As was also mentioned, the mass of the ar10 bolt is large and could push the bullet forward with inertia if the bullet is not held enough. Think of an intertial bullet puller. Try loading the cartridge in the chamber and then closing the bolt but worrying about 3 thousandths for a gas gun is a waste of your time.

 

[stork]

Just an FYI, you may want to test your crimped vs uncrimped loads.
I just did so & found uncrimped to give better accuracy across the board with 3 AR's & 2 bolts (Tikka & Howa).
As I do not own semi autos larger than 223, recoil isn't a factor but accuracy is, for me anyway.
Stork

 

[ebb]

Ive never crimped a bullet shot out of my AR10, never seen the need. Why did you decide to crimp am I missing something?

 

[Jeff Porter]

I use neck tension rather than crimp to keep them in place. That said - if you are feeding from a magazine and the 0.003” takes you “out of tune”. Check your load or use another bullet that is more forgiving. If you are single loading , push the case into the chamber before you drop the bolt. Minimizes the impulse and the “ using the chamber as a sizing die” effect.