I bought a middy 5.56 upper and did some component swapping around Black Friday changing my AR lineup a bit. That left me with an extra upper receiver, and all the carbine length components off my former m4gery’s upper. I’d been talking with some buddies about the other caliber options for AR’s and had been very interested in 7.62x39, but didn’t like how bolts weren’t holding up in that configuration.
So in my quest for knowledge, I ended up seeing some ballistics for the 300blk, and then learned that everything but the barrel was regular 5.56 parts - that meant I could add a caliber for the cost of a barrel and the dies to make the ammo. I was in.
As we all know, plans are only good until the first encounter with the enemy, and my 300blk build was no different. I went from using entirely surplus parts, to an almost full on custom build. The upper receiver will be the only “used” component in this gun when all the build parts arrive. ![]()
So for now, we have a CMMG upper, 16" DD 1-8 CHF carbine gas system S2W profile barrel, Troy vtac alpha forearm, ADM scope mount, and Zeiss Conquest 4.5-14x50 scope.
I have it on my m4gery lower at the moment, but have a JD lower, PSA LPK, Double Star AFX stock, and brownells stock completion kit ordered for it, and if they ever come back in stock it’ll get one of the Spikes BCG’s I have backordered.
With the CTR buttstock, it weighs in right around 9#.

The only shooting I’ve done so far was some function test loads @25 yds, but here’s 10 rounds of 150gr SMK’s.

So far, I like it!