CMMG barrels and headspace

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eastern_hunter
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CMMG barrels and headspace

Post by eastern_hunter » Sun Apr 28, 2013 11:58 am

Guys,

I have a 16" upper w a Paladin barrel that works fine.

Have been playing with an 8.5" CMMG 1:7 Wasp bbl fitted to a Bravo Company flat top upper and a YHM middy length Light Rail. The tube has a TROS 5/8x24 to 3 lug adapter that just gets the nose of the barrel assembly out of the forearm. This upper is to be used on an RR Bushy M16.

Have used the BCG from the 16" upper with the shorty upper. That BCG is a carrier and bolt bought from Brownell's many years ago.

Had a BCM M16 hard coated carrier in the spares box, and was recently able to get a complete Stag 5.56 bolt to complete it for shorty 300 BLK. I prefer that uppers have their own BCGs so they can wear together.

Question for you all is: I don't have a set of headspace gauges for 300 BLK. If I use subs to fireform newly made brass, are there significant risks to firing the shorty upper w the Stag bolt? Anything unusual about the Stag bolt in comparison to a CMMG bolt?

Thanks!

Mike

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AR-300
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Re: CMMG barrels and headspace

Post by AR-300 » Sun Apr 28, 2013 7:41 pm

rent the gauge set here: http://www.4-dproducts.com/displayitem. ... ame=rental
$8 charge, $80 deposit
make sure to get the set and if the go goes
and the no-go doesn't, you are good!
PSA 10.5" & 16'' FN CHF CL 300 AAC Blackout

eastern_hunter
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Re: CMMG barrels and headspace

Post by eastern_hunter » Tue Apr 30, 2013 9:29 pm

Have rented reamers from 4-D, but didn't realize they also rented gauges for some reason. Thank you for the reminder!

Checked the rifle the not so sensible way. Headspace is fine with the Stag bolt. Gas port is not big enough and the rifle is short stroking enough that it is not picking up the next round in the magazine even with a standard buffer and spring.

So will work out the subsonic load with chrono and open the port to get it to cycle completely.

pman5kmo
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Re: CMMG barrels and headspace

Post by pman5kmo » Thu Jun 27, 2013 1:50 pm

eastern_hunter wrote:Have rented reamers from 4-D, but didn't realize they also rented gauges for some reason. Thank you for the reminder!

Checked the rifle the not so sensible way. Headspace is fine with the Stag bolt. Gas port is not big enough and the rifle is short stroking enough that it is not picking up the next round in the magazine even with a standard buffer and spring.

So will work out the subsonic load with chrono and open the port to get it to cycle completely.

Midway has bolts in stock, and some carriers and assys... I was sharing the carrier with dedicated bolts in each. I wound up getting another carrier later that was NiB treated, and the other bolt I have is a NiB treated 'super bolt' so now the carriers and bolts are very distinguishable between all my ARs and uppers.

The sub's you're using, factory or hand loaded?

If loading your own you need to use much slower powder than H110 or lil' gun... Something like A1680 or AA5744, I have had excellent results with both with 1680 just being a tad more consistent in velocity. my cmmg 8.5" barrel cycles supers well and subs just fine even with an extra heavy buffer and spring that i use for my Mk12 upper (made velocities of mk262 clone loads much more consistent and less gas blowback when suppressed) as many have said this barrel tends to over gas with supers. My sub loads cycle just fine and lock bolt 9/10 times. Never short stroked with either AA powder and running at 1025fps w/1680 and 1035 with 5744. I havent been avle to get my hands on factory subs yet.

Boosted98gsx
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Re: CMMG barrels and headspace

Post by Boosted98gsx » Wed Aug 14, 2013 1:01 pm

I'm in the process of building an SBR with this barrel. Following for progress.
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