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New to .308 in GA


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Just started the process of assembling an AR in 308. As for why? The Readers Digest version is because I "need" one of course. I have lots of AR's in 5.56, 300Blk and even .50Beo, but am looking to stretch my shooting legs a bit. Truth be told, I bought a Burris Eliminator III for a 20" BCM and realized it's too much scope for 5.56 so let's build a rifle around the scope hence the .308 project.


Starting with a CMMG MK3 18" upper assembly and am eyeing an Aero complete lower. I will replace the trigger with an SSA I have laying around, the pistol grip with a BCM MOD 1, the charging handle with a BCM Mod 4.


The question I have centers around the buffer tube. I would like to go with either a UBR or PRS. Springs and buffers are specific to .308 but what about the tube itself? Can I use a rifle length (or carbine length for that matter) buffer tube from a 5.56? I have googled and searched several sites but never found a definitive yay or nay on this. 

Edited by thenorsepole
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Welcome form AZ!!!!


Some here would discourage you from getting a CMMG, but it looks like you have some experience wrenching with the rifles so you will be good to go IMO.


The CMMG MK3 platform is good to go. You should give it the once over before you take the first shot though. It's not uncommon to find that the barrel nuts aren't torqued down tight enough on them.

Edited by shibiwan
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Roger that shibiwan. I checked the upper out as soon as it was unboxed - looks like someone at CMMG was doing their job that day. Perhaps a new hire? Barrel nut is nice and tight from what I can tell without the tool. Once I get the tool in my hands I'll will re-torq so I can see it with my own eyes. Keymod handguard was nice and tight although I did pull out the stick of blue locktite for my own peace of mind. Seems like a good upper for the price although it's just a honking chunk 'o metal until post-Christmas allows for the lower.


I will get another BCG for it and use the stock BCG for backup/parts.   

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