CMMG 8.5" 300blk

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tgbrowning
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Re: CMMG 8.5" 300blk

Post by tgbrowning »

I bought several of these barrels for our shop. Fit and finish is excellent. As others have stated, the barrel is dimpled for the gas block, so alignment of the gas block was as simple as it gets. So far, all I have fired are Remington 220 grain subsonic loads. Function and accuracy have been 1st class. I will be hand loading this round in the very near future, using 110gr Hornady V-Max, 125gr Sierra OTM's and 220gr Sierra OTM's, mostly because I already have them in stock. Another bullet that has my eye is the Speer 125gr TNT. Looking at load data posted, it appears the 125gr bullets are just about ideal for my intended uses.

Terry
Bullit Proof Arms
Buda, TX.
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nolwark76
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Re: CMMG 8.5" 300blk

Post by nolwark76 »

How is everybody liking the CMMG 8.5" complete upper? I was completely sold on the PWS piston 9" upper until I RSilvers said basically they weren't cleaner than DI. He also said that the DI was cheaper, lighter, and quieter. Why go piston then? I can maybe see it if you weren't going to suppress it so your bolt carrier was cleaner but since I am going to run a can, the piston will still get dirty. I think the CMMG is priced right.
Taseal
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Re: CMMG 8.5" 300blk

Post by Taseal »

nolwark76 wrote:How is everybody liking the CMMG 8.5" complete upper? I was completely sold on the PWS piston 9" upper until I RSilvers said basically they weren't cleaner than DI. He also said that the DI was cheaper, lighter, and quieter. Why go piston then? I can maybe see it if you weren't going to suppress it so your bolt carrier was cleaner but since I am going to run a can, the piston will still get dirty. I think the CMMG is priced right.
piston IS cleaner. with supperssed, both run dirty, but piston will be cleaner

just think about it.... in a DI system, the gas goes to the bolt where most failures happen

on a PWS long stroke piston, it is nowhere near there, so very minimal gas gets in there to gunk it up with carbon.

It's just how it is. when suppressed they will both get dirty, but DI will get dirtier. (all that backpressure)

it becomes a he said she said, so take it as you will.

you did mention you'll run it with a can. with a piston, it'll get dirty. with DI, it'll just be dirtier. but then again, perhaps the twice the cost isn't much of a factor. I will say PWS CS is second to none. CMMG is pretty much non existant from what I have read here.
Poppy83
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Re: CMMG 8.5" 300blk

Post by Poppy83 »

I was itching for a piston AR because of the "cleaner" issues. I thought about it for about 10 seconds and realized that I'm familiar with a DI AR and I can just spend a little more on a BCG. I bought a Spikes NiB BCG and it wipes right down.

I SBR'd a Sig 556 to get my piston fill...
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Uvausmc
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Re: CMMG 8.5" 300blk

Post by Uvausmc »

nolwark76 wrote:How is everybody liking the CMMG 8.5" complete upper? I was completely sold on the PWS piston 9" upper until I RSilvers said basically they weren't cleaner than DI. He also said that the DI was cheaper, lighter, and quieter. Why go piston then? I can maybe see it if you weren't going to suppress it so your bolt carrier was cleaner but since I am going to run a can, the piston will still get dirty. I think the CMMG is priced right.
I love mine. Ive only shot 110 gr VMax and 125 SP through it but accuracy was good and reliability was 100%.

Image
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donald150
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Re: CMMG 8.5" 300blk

Post by donald150 »

I just picked up one of these 8.5" barrels mine has the 1/8 twist and i have a couple of questions.
I see some gas blocks sold as 5.56 and some as AR-10, does it matter? do i use the AR10
block or any block that is .750"?

what about adjustable gas blocks, i do not have a supressor and shoot mostly supersonic but do shoot some subs.

should i use an adjustable gas block? it couldent hurt if i did right?
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tgbrowning
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Re: CMMG 8.5" 300blk

Post by tgbrowning »

As long as the gas block fits the barrel, it will work. I built mine using a low profile gas block that fits under the handguard. I change to a heavier buffer for lighter bullets fired at higher velocities.
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donald150
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Re: CMMG 8.5" 300blk

Post by donald150 »

I decided to go with a Seekins Precision Adjustable Gas Block from joebob outfitters.
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I also ordered a Daniel Defense Muzzle Climb Mitigator Muzzle Brake.
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Here is what it looks like so far. It used to be a 5.56. pistol w/10.5" barrel but I took off that barrel to put on the 300AAC.


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eastern_hunter
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Re: CMMG 8.5" 300blk

Post by eastern_hunter »

What is the diameter of the barrel at the place the gas block mounts?

Thanks!
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donald150
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Re: CMMG 8.5" 300blk

Post by donald150 »

eastern_hunter wrote:What is the diameter of the barrel at the place the gas block mounts?

Thanks!
.750
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