Brass Life in AR-10?

[Phil3]

I am building an Armalite AR-10(b) rifle and was wondering about brass life.  I ask because I wish to use the 6.5 x 47 Lapua cartridge, which I will reload.  The only brass is Lapua, which is expensive, so if the AR-10 tends to beat it up badly and give me short case life, I may have to move to a cartridge where there is cheaper brass (i.e., 6.5mm Creedmoor).  I would likely have the barrel chambered by Krieger to fit my bolt and upper receiver (Armalite).  

Thanks,

Phil

[98Z5V]

You're building a 6.5x47 Lapua, just in a semi-auto.  It would be better to try to find out the brass life of that cartridge, through bolt guns - which they mostly are - then try to find out if there is a difference in brass life between bolt guns and semi-autos (there definitely is, but I'm not sure if there's a calculation or number to assign to that - a percentage).  

If you're reloading, and only for one gun - you can get some incredible brass life based on your reloading practices.  Reloading the same caliber across multiple rifles - brass won't last as long.

Are you working with this rifle here - with a new barrel? - or is this a completely different gun now?

 

[edgecrusher]

I thought he wanted to re size the brass to .308.... had to re read that

[Sisco]

Can’t speak for anything but 308, but my AR10 B models actually are very easy on brass. I don’t load close to SAAMI max, and that probably has a bit to do with it. So far I have some M80 generic brass on their 4th reload and still looking good. Like 98 said, the pressure endemic to the cartridge probably has more to do with brass life then the platform, unless you have built a custom brass shredder rather then a larger caliber AR.

[Phil3]

I am the OP.  In answer to questions...

I am building a 6.5 x 47 bolt gun AND a 6.5 x 47 AR-10.  That was the plan, unless the AR beats up pricey 6.5 x 47 Lapua brass (hence my question) at a rate that becomes unacceptably expensive. 

The 6.5 x 47 Lapua brass can last a long time in a bolt gun, no worse than anything else, but its max pressure is 63,091 psi, which is slightly higher than the 62,000 psi for 308 and 6.5 Creedmoor.  As such, the 6.5 x 47 Lapua can work the brass a tad harder. 

I do not know how much brass life is shortened in a semi-auto vs a bolt gun.  Knowing that would certainly help.  I would keep the brass for the AR-10 separate from that of the bolt gun.  I will be using a custom honed full length sizing die for each gun and the brass that it uses.  This will minimize working the brass and prolong brass life.  I will also be annealing the cases every few rounds to further extend brass life.  

I have no desire to load to high pressures, so hopefully that will help with brass life.  At around $1.20 each for the 6.5 x 47 Lapua brass, I cannot afford to have cases ready for the trash after just a few uses.  If the AR-10 eats cases for breakfast, I will need to move to another caliber where cheaper brass is available (6.5 Creedmoor, 308 Winchester, etc.).  

Thanks,

Phil

[Sisco]

I can only go with my personal experience with two AR10 B’s that were unmodified from the factory, and each has in the vicinity of 1,000 rounds through them, mostly M118LR or equivalent and M80 standard NATO. Neither has ever excessively deformed or tore brass. Once you change barreling I can’t say what will happen. I suggest checking the archives to see if any one has reported AR10 brass deformation in the past. Good luck, it sounds like a very interesting build.

[98Z5V]

For Big ARs, I reload .308 in 3 of them, .338 Fed for one, and .260 Rem for one - those guns don't eat brass.  If I'm shooting the bolt gun at the same time, I can't tell which brass came from which gun, honestly.  You build something overgassed or under-recoiled, where the BCG is cycling way too fast - and that's gonna tear up brass.  Build it wisely, and it shouldn't be an issue at all...  My $0.02. 

[Phil3]

Thanks for the comments.  I would like to ensure the gas system and BCG are cycling properly (proper parts and design) so as to avoid eating expensive brass.  I may ask for some advise on that.

It should be an interesting build, although cannot be exactly what I want because I am in California, with some quite absurd restrictions.  I got some parts 9 years ago, so it will be kind of a retro build (Armalite AR-10b).  

Phil

[Cliff R]

No reason that I know of why the platform would effect case life unless the barrels chamber was out at max specs and your reloading dies at minimum.  That would cause maximum expansion, stretching, thinning and lengthening the cases with each use..

You will loose one here and there unless you put a big sheet or blanket out on range days as they throw the brass out there a bit.

Over the years I've found the hardest thing on brass is pressure.  High pressures knock out the primer pockets to a point where they don't have a tight enough fit for the primers but the rest of the brass is sound.  Really excessive pressures can cause case separations.

I've been reloading since the mid 1970's and tend to avoid really fast powders and pushing things up near the limits.  I've only ran into pressure issues and short case life a couple of times, and that was with 22/250 and 6MM Remington.  Federal brass back in those days was pretty much garbage, at least in 22/250.  You'd be lucky to get more than 3 reloads out of it if you were pushing things pretty hard. 

For bolt guns you can back the dies off some if always using the same rifle.  This helps to improve case life and accuracy.  For autoloaders that deal doesn't work as well so the cases will get resized then re-expand with each use, and require trimming in between as they will grow slightly from being worked.

I've never tried annealing cases although I do know about it.  Seems like a lot of extra work but might be worth it at $1.25 each to replace them.......Cliff

[HotRod308]

The biggest tip for long brass life is to is not to over work the brass during the reszing process. Buy a case measuring tool and measure the fired case and only resize only .002 to .003 smaller than the fired case measurement. Use a bushing die so that neck is only reduced to the correct amount of neck tension usually .001 (kind of light tension) .002 (medium) anything after that is a lot of neck tension and you are over working the brass. The expander button will thin out the necks over time which is why you have to trim the brass back to correct length. I use .002 neck tension for ammo feeding from the mag and ,001 for single loading for slow fire stage at 600yds. 

Higher pressure loads, the case will measure a little bigger than normal loaded round. Faster powders are harder on the brass than slower powders.

I quit counting how many reloads I get out of any of my big AR's I load for, but it's probably around 15 to 18 reloads before I get rid of them. Usually the primer pockets get to loose or once the neck thins out they start to crack.

 

Don't worry about it, just set up the dies correctly and it will be fine.

[Phil3]

Thanks for tips on reloading.  My reloading equipment is good quality and complete, so I think I am well positioned to take best care of the cases.  I use Quickload software, chronograph, along with visual inspection to avoid excessive pressure.  If I can get 15 - 18 reloads out of brass, I will be quite happy.  I will be using a Forster Co-Ax press, and most likely Forster dies.  A friend has an annealer and he will anneal cases for me as I require.  

I will see if I can determine the reamer used to cut the chamber, or at the minimum, have a full length die honed in the neck area to resize the neck to the exact size I want for desired neck tension (.002"), negating the need for an expander button, while also maintaining proper neck clearance in the chamber (.003").  I do not want a loose chamber as the neck will expand excessively upon firing, working the brass, hence my desire to know reamer dimensions.  

From what is said here, it seems like my Lapua brass will have a decent life in the AR-10 and helps with my worry over the gun beating it up and forcing frequent buying of new brass.  I am after accuracy, not ultimate velocity and do not expect to be pushing pressure limits in the pursuit of velocity.  The brass for the AR-10 will only be used in that rifle, not my bolt gun. 

I have some questions on proper gassing of the system, with regards to barrel length, gas port placement, custom barrel extensions, buffer components, etc.  For another thread.

Thank you.

Phil

[98Z5V]

7 hours ago, Phil3 said:

I have some questions on proper gassing of the system, with regards to barrel length, gas port placement, custom barrel extensions, buffer components, etc.  For another thread.

Thank you.

Phil

Get into that when you want - start that thread whenever you want.  I can go over alot of the problems in the past, and info that we've gotten from these platforms.  Some things work, and some things definitely do not work.