Do AR chambers/mags handle the longer projectiles?

[ScreamingPotato]

A nice bolt action .223 has been on my radar for a bit, specifically looking to shoot the 77gr TMK, or the heavier ELD-M's and such. I already own too many ARs and they just sit. Got to thinking I can simply buy a longer match barrel or see how they shoot in my 16" 1/7 twist barrels even. Are the standard "milspec" chambers and mags able to handle the longer OAL from ammo such as these? I know this has already been covered probably multiple times but my searches are bringing up so much clutter it's difficult to sort through.

 

[E.Shell]

Factory loaded ammunition (AAC, Black Hills) is loaded short enough to function with standard chambers and standard length magazines. I'm loading 77 TMKs at SAAMI max length (2.26" per the handloading manual) and they cycle through AR-15 magazines just fine.

If you had longer throat and magazine capacity and handload, you could squeeze a little more velocity out of the longer/heavier bullets by loading them a little longer and gaining a little powder capacity.

I have a few AR-15s too and a bunch of magazines and ended up buying the Ruger American Ranch bolt gun in 5.56 so I could use my existing magazines, ammo and components.

 

[ScreamingPotato]

Thank you! I'm gonna try to pickup a quality barrel and get a dedicated scoped upper setup and see how it shoots with factory AAC 77gr. Good tip on the Ranch though, might be an option if I'm not shooting well with the AR.

 

[KyleR1985]

77’s as described above work great. My experience has been 2moa or better off the bench with a 16” barrel. 1-7 and 1-8.

If you want to get them to go faster, or potentially tighten accuracy, you’ll need to do a few things:

- have reloading equipment

- have windowed magazines to allow longer COAL. You can cut steel ones yourself, or buy from PRI already modified. This gets you to 2.35” minimum.

- your specific mag well will be the next limiter on COAL. They’ll allow COAL ranging from 2.35”-2.39” as is, from what I’ve seen. You can file a channel in the front of your mag well down to as thin as you’re comfortable with. This can get you up to 2.40”-2.45” COAL.

- your upper and barrel extension are the next limiter. They’re going to allow COAL 2.35”-2.40” as is. You can continue the channel you filed in your mag well up through the upper receiver and barrel extension. You’ll want to disassemble to do this. But you can get the upper and extension filed back to allow 2.45” COAL without compromising bolt and lug performance.



Doing All of the above will get you the ability to run the really long bullets like the 88’s. It’ll get you the ability to seat the 77’s at or close to the lands. And it’ll get you 50-200fps by allowing more case capacity.


I think most people will not want to permanently modify their modular rifles. The windowed mags are a big improvement for low cost, if you reload. Seating depth flexibility and almost a tenth of an inch of case capacity are big.

 

[KyleR1985]

Or just get a 22ARC and get everything discussed above in 2.35” or less…

 

[Thegman]

You may want to just try starting with a magazine that allows loading a little longer. My Duramags allow 2.318" and so far have been doing okay with 75+ ELD-M and a FCD in a 1 in 7 twist. Your barrel(s) may shoot them okay or better than okay at that length. Just have to try to find out. I might try windowing at some point, but so far haven't really needed to with my current barrel.

The 75+ ELD-M bullets seem to produce less pressure and more velocity than their weight/bearing surface might suggest, in a 5.56/223 Wylde AR barrel, anyway. That may be due to how long the AR barrel throats are, in general. Due to their shape, these bullets in my barrels are pretty far out (like ~ 2.5") before they contact the lands and offer more resistance to increase pressure. I'm guessing that may lower peak pressure below what one might initially estimate.