Picked up an Aero M5 upper and lower and I guess I've settled on the 308 instead if playing around with 6.5 Creedmoor. Gonna he honest here have no idea what the purpose of the gun actually will be. Other than I have zero history with a large frame AR. I do have enough reading to know there is no standard which is why I went with the same upper and lower.


My question is...  should I do a standard A2 stock or go with the UBR?  I like my ubr on my 12" AR15 SBR.  But also like my 18" SPR with the A2 stock.


If I had to guess right now I might take this gun hunting.


And will a standard Ar15 rifle extension screw into the M5 extension area?


But here's my build sheet so far:

Aero reciever set

Faxon 308 barrel (I think it's the gunner profile?)

Aero M5 LPK and adding an RRA national match trigger

Aero BCG but might consider a cheaper option.


Just need guidance on the stock before moving on to handguard and optics.

LOP is longer on large frames compared to a AR-15. A2 stocks end up having too long of a LOP for a lot of people. A1 stocks might be a better choice if you go with that sort of stock. Receiver extensions are the same as a AR-15. The UBR is a solid choice. They use a proprietary intermediate length (A5) RE. You'll need different buffer and spring set-ups for the two options you listed.

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Blue arrow is M5 with A1 stock. The lop was too short in prone for my preference so I switched it out with an A2.

Either way, it functions much better with the rifle buffer system than it did with the carbine tube and carbine 308 buffer/spring. I had problems with gas, especially going from suppressed to unsuppressed. With the rifle system it is much more forgiving.

Be sure to get the Armalite AR-10 gas tube for your Faxon 308 barrel.  not sure what gas length you got, but if it's the mid-length gas option, you'll need the Armalite AR-10 Carbine gas tube.  That's how Armalite defines their AR-10 carbine length.  It is what it is.

If your Faxon barrel is rifle-gas, then it's the Armalite AR-10 rifle-length gas tube.  the AR-15 gas tubes are about 3/16" shorter than their Armalite AR-10 counterparts.

I usually get my Armalite AR-10 gas tubes direct from Armalite, 'cuz then you know it's correct.

The Brownells nitride 308 BCG is GTG, has the beveled edges at the back end of the major diameter, like the Aero BCG.  and also has the skinnier HP firing pin, and corresponding smaller firing pin aperture in the bolt face.  But the Aero 308 nitride is GTG also, might be $10 or $20 more.  shop around.

Aero M5 handguards are the easy choice.  check their "blems" to save money.  otherwise just make sure you get the DPMS-high.

adj gas blocks are highly recommended for the large frame AR.  I use SLR, but a lot of folks like the Superlative.

Faxon uses DPMS not Armalite gas tube lengths, so you'd want an AR15 gas tube, not an Armalite AR10 gas tube.


https://faxonfirearms.com/ar-gas-tube-rifle-length/

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I like the UBR in my .308

@Daggertt

here's my Faxon 308 barrel with an AR-15 rifle gas tube, in my DPMS-pattern AR-10 upper receiver (Aero M5).  subsequently replaced with an Armalite AR-10 gas tube.  I've found this to be the case from doing several 308, 6.5CM Faxon barrels builds: Gunner, Heavy Fluted, Medium Taper.  Armalite is usually out-of-stock on their AR-10 gas tubes, so ...

YMMV.



ETA:
I should add, I'm not a Faxon fan boi.  I also use Criterion, BA, Rainier, Brownells, KAK barrels for my AR-10 builds.

UBR 2 will let you use the variety of AR15 carbine buffers.  It also packs shorter for moving about. I'd go with that.

OP, Very similar build to yours.

Thanks for the info guys actually helps a lot!

As I said I am aware of there being no standard across the board.  The Brownell seems to have their BCG at a lower cost, will they definitely work in the M5 upper?  


Also in regards to DPMS height handguards are there any particular brands I should I look at?


Seems I'm gonna go with the UBR as I like the two photos posted with them. I was wanting to go rifle length for sure. I was thinking about the UBR using the A5 tube length I believe I should go with a LaRue Spring or SpringCo Red with an H3 carbine buffer?  Does this sound right?


I also forgot to add something important!  Will be suppressed when my 30 cal can is out of ATF jail.

I like the Armalite EA1095 springs, very God and cost effective.  I run an H3 or H2 depending on the gas length.  H3 is probably good for 90% of the AR10s out there.

Well shit if they're God imma buy that!  I know what you mean. I'll look into them. Parts should be coming in slowly over the next couple of weeks. My wife is going on vacation with my mom (weird) in two weeks so that's when I'll really be able to start the actual build.


Will post pics!

i have a Luther fixed rifle stock on my AR.308 and love it.

I went with the UBR on my .308.  I am quite fond of the SLR forends.  I actually built an entire SLR rifle on their large frame receiver.  If you're going to suppress the gun, get an adjustable gas block.  You will need it.

nice build.  nice rail.  made out of Unobtainium, right?  nice.  

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i use gen 1 ubr on my 16" i used quad rails so the ubr helps balance weight.

front heavy ar10s arent fun, my 10.5 told me that

TY, yes, little did I know when I bought that rail as an open box rail many years ago how special it would be.  I'm big on the KAC FF RAS/Quad Rail approach and was looking to build out both a MK11 Mod 1 clone (I have the rail!) as well as a more generic/"general purpose" AR-10.  So years ago I started picking up the parts ala carte and then early last year, in the early days of the pandemic lock down, I decided to do a build of the "general purpose" 308 rifle to give myself some AR-10 style options (you think that rail is unobtanium, try building a MK11 close...ugh).   It shoots great, is not too heavy and overall I'm very very surprisingly pleased with it. Similar manual of arms as my AR-15's, etc too.

It deserves a better, higher quality optic as well as a suppressor.  The Warcomp works great, very little muzzle rise vs the standard A2 style that I originally had on it.  And I sighted it in using some bulk 168g 308 ammo, but need to pick a quality supply of either 168 or 175 going forward.  Tough to find, so I've really not shot it much to conserve ammo.

I'd like to build out a 20" as a secondary AR10, and as much as I want to build the MK11/M110 style rifle, the cost, parts and assembly/fitting issues are just a big pain in the ass when on a limited budget.  So a second generic rifle, maybe MK11 inspired by using the MK11 Mod 1 rail, will be the result.  No budget for that right now.

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UBR is mo betta.


Edit- no idea why the pic isn’t showing up.

Update


Digging through my stuff I may have a 15" SR25 URX 4 that I have no idea how I got it.


Thus thread will probably turn into the let's build a battle rifle thread.

UBR
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I'm not a fan of the UBR, but I love the STR stock. Much better cheekweld for me. I have four of those, and the rest are CTRs.

STR guy here too.  All of my AR-15's, well carbine style/size, have STR stocks.  I really like it over the B5.  I have not used the UBR as much as any of the STR's, but I've found it to be comfortable and I really like it more than I thought I was going to.  I might get the thicker butt pad for it someday, long bench sessions can wear on you, but its all sighted in now.

Yep I went STR as well.

Yep. I've used B5s before and did not care for them. Limbsaver makes a pad that fits Magpul stocks. I have two- one on each precision AR- not for recoil mitigation per se, but a better grip on my shoulder when prone and to help make it easier to stay on target.

A1 with a Limbsaver.

UBR most definitely

I went with B5 SOPMOD on an Vltor A5 receiver extension. UBR looks nice, but couldn’t justify the cost.

Alright thanks for the input guys!  I seem to have an issue with jumping between projects. I want to get my 11.5" sbr finished and then I'll dedicate more time to this. I like the B5s on my AR15s. What I'll do is just try the different stocks mentioned in the thread. If you guys want to tag or subscribe I should be posting pics and starting the M5 in just two weeks (no irony intended).

Limbsaver pad that fits the UBR2

https://www.nokick.com/Limbsaver_Recoil_Pad_for_Magpul_SL_Stocks_p/ls-10829.htm

Combined this with an adjustable gas block and it's soft and smooth