CMMG 8.5" 300blk

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eastern_hunter
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Re: CMMG 8.5" 300blk

Post by eastern_hunter » Tue Dec 18, 2012 3:58 pm

Excellent!!!!

Thank you ...

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shooterready
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Re: CMMG 8.5" 300blk

Post by shooterready » Sun Feb 17, 2013 8:36 pm

I just finished my 300BLK upper with 8.5" CMMG barrel. Port size was .096" and would not lock bolt with 190gr subs and Noveske KX3.

I'm running a Syrac Ord. adjustable gas block. I took port size to .125" and now reliably bolt lock on last round with the 190gr subs I have. Gas block full gas. .110" was just not enough.

I worked a 9.0gr Lil-gun load up for a 145gr M80 projectile and could lock bolt reliably. 8.0grs would not. Win SR primers, trim length 1.358". Seated to cannelure groove.

Still need to speed these, but believe these are sub given comparison to 190 factories that I have.

I've got a ton of M80s and want to run subs without a can. Can is in the future, but distant at best.

Just glad I decided to build this project quite a few months ago when you could actually get parts.
300BLK CMMG 8.5" 1:7 barrel
Pistol length .125" gas port
Syrac Ord. adjustable gas block
Noveske KX3 flaming pig

sdacbob
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Re: CMMG 8.5" 300blk

Post by sdacbob » Sat Oct 26, 2013 7:26 pm

Just back from the range. Tried out my new factory 8.5 upper with some Summit 147gr rounds. Used my Spikes ST2 buffer in a pistol lower. Bolt locked back on empty P mags, worked great, no issues.

jwb47
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Re: CMMG 8.5" 300blk

Post by jwb47 » Sun Nov 10, 2013 3:15 pm

well I'm a little late for this party . I put my 8.5 together back in january . it is an 8.5 cmmg 1/7 twist barrel with a pri low profile gas block under a midwest industries 7 inch had guard mated to a brass aluminum forgings upper . the buffer tube I dont know it was in a bag with a carbine buffer and spring and looked good . lower is a seekins precision with cmmg lower parts kit yankee hill phantom suppresor with qd mount and an aimpoint pro. all on a sesame seed bun. I mostly shoot 225 grain hornadys over 10.4 grains of 1680 or outlaw state 220 grain expanding subs for hunting with the same powder charge .

to be honest I can do 1.5 inch groups at 50 yds and 4 inch at 100 yds which is a function of my old eyes and no magnification not the rifle.
I have shot 110 grain v-max with no issues but did not build this for supers so I dont have much info on a steady diet of such.
I just recently added the sig arm brace and am so far liking it.
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Overton-AR
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Re: CMMG 8.5" 300blk

Post by Overton-AR » Sun Nov 10, 2013 6:12 pm

This is the barrel I am leaning towards for my new shorty upper I am building.
I was going to go with the Rainier, but its a 1x8.5" twist and I really want a faster
twisting 1x7. I shoot 220 grain subs about 90% of the time and I worry about
them stabilizing in the slower twist.

All I lack for the build in the barrel and gas tube.....so I need to decide quick.

Boosted98gsx
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Re: CMMG 8.5" 300blk

Post by Boosted98gsx » Mon Nov 25, 2013 12:44 pm

I recently built my SBR out of this barrel. LOVE IT. Just got my Form 1 back Nov 5th, so I can finally post pictures.

Image

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It cycles supers and subs, can or not. Gas port size is standard, and an off the shelf YHM clamp on gas block, off the shelf standard tube, with a standard carbine buffer. That's a JP fore end as well.
Last edited by Boosted98gsx on Mon Aug 18, 2014 1:47 pm, edited 1 time in total.
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eastern_hunter
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Re: CMMG 8.5" 300blk

Post by eastern_hunter » Sun Feb 16, 2014 10:16 pm

After getting the SBR stamp back I built an upper with the 8.5" 1:7 CMMG bbl. Planned the upper for subs only as I have a 16" upper for supers and subs. Put a TROS 3 lug adapter on the bbl and used a 9.5" YHM light rail. Opened the port to 0.120"

Works fine with my SBR lowers and 8.5 gr 2400 driving 225 gr Hornady OTMs fired with WSR primers. Octane 9 and Octane 45 cans quiet the little rifle pretty well ... easily hearing safe.

Kinda looking forward to popping the upper with an Octane 45 mounted on a registered M16 lower and using the giggle switch ;-)

Boosted98gsx
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Re: CMMG 8.5" 300blk

Post by Boosted98gsx » Sat Mar 01, 2014 1:59 pm

eastern_hunter wrote:After getting the SBR stamp back I built an upper with the 8.5" 1:7 CMMG bbl. Planned the upper for subs only as I have a 16" upper for supers and subs. Put a TROS 3 lug adapter on the bbl and used a 9.5" YHM light rail. Opened the port to 0.120"

Works fine with my SBR lowers and 8.5 gr 2400 driving 225 gr Hornady OTMs fired with WSR primers. Octane 9 and Octane 45 cans quiet the little rifle pretty well ... easily hearing safe.

Kinda looking forward to popping the upper with an Octane 45 mounted on a registered M16 lower and using the giggle switch ;-)
Without another stamp (to SBR the M16), I wouldn't recommend it.
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Outsydlooknin
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Re: CMMG 8.5" 300blk

Post by Outsydlooknin » Sat Mar 01, 2014 4:18 pm

Boostedknow the NFA 98gsx wrote:
eastern_hunter wrote:After getting the SBR stamp back I built an upper with the 8.5" 1:7 CMMG bbl. Planned the upper for subs only as I have a 16" upper for supers and subs. Put a TROS 3 lug adapter on the bbl and used a 9.5" YHM light rail. Opened the port to 0.120"

Works fine with my SBR lowers and 8.5 gr 2400 driving 225 gr Hornady OTMs fired with WSR primers. Octane 9 and Octane 45 cans quiet the little rifle pretty well ... easily hearing safe.

Kinda looking forward to popping the upper with an Octane 45 mounted on a registered M16 lower and using the giggle switch ;-)
Without another stamp (to SBR the M16), I wouldn't recommend it.
He is fine.........machine gun trumps SBR.

Might want to know the NFA laws before you spout off more falsehoods.

Boosted98gsx
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Re: CMMG 8.5" 300blk

Post by Boosted98gsx » Sat Mar 01, 2014 4:22 pm

Outsydlooknin wrote:
Boostedknow the NFA 98gsx wrote:
eastern_hunter wrote:After getting the SBR stamp back I built an upper with the 8.5" 1:7 CMMG bbl. Planned the upper for subs only as I have a 16" upper for supers and subs. Put a TROS 3 lug adapter on the bbl and used a 9.5" YHM light rail. Opened the port to 0.120"

Works fine with my SBR lowers and 8.5 gr 2400 driving 225 gr Hornady OTMs fired with WSR primers. Octane 9 and Octane 45 cans quiet the little rifle pretty well ... easily hearing safe.

Kinda looking forward to popping the upper with an Octane 45 mounted on a registered M16 lower and using the giggle switch ;-)
Without another stamp (to SBR the M16), I wouldn't recommend it.
He is fine.........machine gun trumps SBR.

Might want to know the NFA laws before you spout off more falsehoods.
Hrm. I was told just today that you had to form 1 it as an SBR. Just did some googling, and good to know.
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