Brass Prep & Trimming For ARs

[sentry1]

When prepping brass for an AR, do you just trim down to the SAAMI max length, or do you use a gage to find out the dimension of your chamber and trim your brass specifically for your chamber?

I found these Sinclair Chamber length gages, but they say they're intended for use in bolt guns.

Sinclair Chamber Length Gage | Sinclair Intl

P.S. I don't expect this to add accuracy, it's just supposed to extend brass life by not cutting it back so much, assuming my chamber is over SAAMI spec length.

 

[BC 6.8]

I set my trimmer up to 0.010" less than SAAMI maximum length.

 

[elfster1234]

http://www.snipershide.com/[email protected]

When prepping brass for an AR, do you just trim down to the SAAMI max length, or do you use a gage to find out the dimension of your chamber and trim your brass specifically for your chamber?

I found these Sinclair Chamber length gages, but they say they're intended for use in bolt guns.

Sinclair Chamber Length Gage | Sinclair Intl

 

[tacguns]

I set my trimmer up to 0.010" less than SAAMI maximum length.

+1 that way you get a couple of firings before you have to trim again

 

[ToddKS]

Due to the volume of trimming involved I purchased one of the Little Crow Gunworks trimmers. It came set at 1.750 which is the recommended trim length in the manuals. .

I highly recommend the LCW trimmer. Not only does it save time on the trimming itself, but it also saves time on the chamfer and debur operations because of how clean it trims the case.

 

[Froggy1129]

Due to the volume of trimming involved I purchased one of the Little Crow Gunworks trimmers. It came set at 1.750 which is the recommended trim length in the manuals. .

I highly recommend the LCW trimmer. Not only does it save time on the trimming itself, but it also saves time on the chamfer and debur operations because of how clean it trims the case.

So are you able to skip debur/chamfer when using the LCW? No issues?

Thanks

 

[insight3b]

I just set my Giraud to trim all that have been bumped back two thou to 1.75 for 5.56mm. If the Giraud cuts more or less on one it gets measured for set-back and the trimmer gets checked to make sure nothing has changed

 

[mtrmn]

Most of the laborious prep used for bolt actions is pointless on AR's unless you're doing benchrest.
Just trim to the recommended length and full-length re-size. I have seen a couple AR's that needed small-base dies to be 100% reliable. Also you are limited to max magazine length on your rounds unless you want to single-feed a semi-auto. So a couple thousandths off the lands is out too.
Despite all these "handicaps" I have never owned an AR that I could not get to sub MOA through load development.
Just don't overthink this and you'll do fine.

 

[ToddKS]

I am not able to skip the chamfer and debur ops completely but they are much easier due to the clean cut. The outside debur is almost non-existent which is a big win. With my RCBS trimmer the burr on the outside of LC brass after trimming was typically fairly significant, with the Little Crow there is almost no burr. Inside chamfer is easier as well.

The unit is so fast on the trimming that I would say my time was reduced 75% overall vs. my RCBS counting all 3 operations. The fact that you just drop the case in and hit the button on the drill is a huge win.

 

[ledavatar]

I don't know if it's worth doing this kind of work for an AR platform, and since it's a semi you want to give it some lee-way so that rounds will chamber properly. If you cut to exact length and then the brass springs back a little, you may jam up your rifle. Not worth it IMO for the potentially little incremental accuracy gain.

In any case, if you're worried about the neck dimensions then you should also be worried about all the other factors of accuracy in making a proper rifle round - neck concentricity, neck turning for proper tension, etc. that really does affect accuracy. Just my 2 cents.

 

[sentry1]

I don't know if it's worth doing this kind of work for an AR platform, and since it's a semi you want to give it some lee-way so that rounds will chamber properly. If you cut to exact length and then the brass springs back a little, you may jam up your rifle. Not worth it IMO for the potentially little incremental accuracy gain.

In any case, if you're worried about the neck dimensions then you should also be worried about all the other factors of accuracy in making a proper rifle round - neck concentricity, neck turning for proper tension, etc. that really does affect accuracy. Just my 2 cents.

Obviously I wouldn't cut it to the exact length of the chamber, I'd cut the brass back .002" from the chamber dimension.

As for the rest of the accuracy factors, they come with a much higher price tag than a $4 gage, so things like neck bushing dies and neck turning kits are farther out on the shopping list.

 

[FLIGHT762]

I set my trimmer up to 0.010" less than SAAMI maximum length.

+1 that way you get a couple of firings before you have to trim again

This is what I do also.

I just set my Giraud to trim all that have been bumped back two thou to 1.75 for 5.56mm. If the Giraud cuts more or less on one it gets measured for set-back and the trimmer gets checked to make sure nothing has changed

This is how I set my Giraud trimmer up. For my.223 AR's, I don't use bushing dies. If I want to prep for accuracy, I use a F/L Redding body die and a Lee Collet die, otherwise, I just use regular RCBS F/L or a S/B die. I've been loading for AR-15's since the early 1970's. My only issue had been to properly set up the F/L die to bump the shoulders back enough to get 100% reliable chambering. Using a case gauge to do this has taken all of the guess work out.

 

[ledavatar]

Obviously I wouldn't cut it to the exact length of the chamber, I'd cut the brass back .002" from the chamber dimension.

As for the rest of the accuracy factors, they come with a much higher price tag than a $4 gage, so things like neck bushing dies and neck turning kits are farther out on the shopping list.

Yes I guess giving it a consistent leeway on the cut would work. One other thing you probably thought of already, but worth mentioning, is that if you have multiple ARs to shoot these out of, then further tolerance need to be made.

Neck turning is a dark, dark art indeed. I've had good success in my 308 bolt gun using quality brass (lapua) without neck turning. That goes a long way, since you're starting from very good base with very little neck runout and more consistent neck thickness. The reason why I mention this is that sometimes people (not saying you) try very hard to turn a turd of a brass into gold but it's much easier to start from a good base.

Good luck, and let us know if you learn anything from it. Thanks.

 

[sentry1]

I only have one AR in each caliber, actually only one rifle in each of the 3 calibers I shoot, so I can tailor my brass for it's specific rifle. My main thought with the chamber length gages was to keep the brass near chamber length, so it's not being chopped short and growing, then being chopped short. I don't think it will add accuracy.

I'll definitely be looking to acquire a neck turning kit for my 6.5 CM bolt gun, and neck bushing sizing dies for that and my .308 AR, but I don't think I'll invest that much more into the .223 AR