CMMG 300 Black Out Uppers

[shadow65]

Just to let you know, the 300 BA uppers are available now:
http://cmmginc.secure-mall.com/shop/?cat=20

[Airhog]

Shadow65, can you explain the pistol length gas system on the 16in. barrel for me. I'm new at building these guns and would like to know the reasoning behind this. Thanks

[shadow65]

Quote from the boss. I've not had an opportunity to test these so I'm in the dark.
"
I am a really big fan of the pistol system. It really seems to meter the gas better than the carbines. Both will work but the pistol seems to be better suited for running largest range of ammo. "

[nhskull21]

Now for ammo.

[Gunpowder]

My impression with AR's has always been that the closer you stay to the original design the more likely you are to have a reliable rifle. So when I see CMMG come out with 16" barrels with a pistol length gas system I am immediately turned off.

I have no doubt CMMG knows more about AR's than I do but I would still like someone to explain to me how this gas system makes sense. Has anyone tried this in a 5.56 with a 16" barrel?

I did notice that CMMG does offer to drill the gas port in the carbine position.

[rsgard]

My impression with AR's has always been that the closer you stay to the original design the more likely you are to have a reliable rifle. So when I see CMMG come out with 16" barrels with a pistol length gas system I am immediately turned off.

I have no doubt CMMG knows more about AR's than I do but I would still like someone to explain to me how this gas system makes sense. Has anyone tried this in a 5.56 with a 16" barrel?

I did notice that CMMG does offer to drill the gas port in the carbine position.

I dont think the 300blk is as high pressure as 5.56N so it would either need a shorter gas system or a lighter buffer. If you want to use the lower for multiple uppers in different calibers why not leave the buffer alone and adjust the gas system to work with the buffer.

[J-Dub]

This is good news for the AR world. The more companies on board with the 300 AAC Blackout the better!

[shadow65]

Burn rates for the different ammo offered is what I understand for the different gas port locations.
CMMG has done the testing on these. Like I said, I'm in the dark on this one.

[JasonM]

gas system lengths can be combined in combination with gas port sizes to balance things out. With a small gas port, a 16" can run well with a pistol gas length.

We've developed our uppers with: 9" and 12.5" uppers with pistol gas, and 16" and 20" uppers with carbine gas.

And agreed, the more companies developing for 300 BLK, the better for everyone.

[SomeOtherGuy]

Great to see these hit the market. As others said, "now for ammo."

Do these barrels have the WASP treatment, chrome lining, or none of the above?

[shadow65]

The barrels are WASP coated.

[Tokarev]

So does anybody have one? The price certainly seems fair.

How's the accuracy with sub- and supersonic? Any reliability issues with the heavy bullets running unsuppressed?

[LonghunterCO]

Burn rates for the different ammo offered is what I understand for the different gas port locations.
CMMG has done the testing on these. Like I said, I'm in the dark on this one.

The 300blk uses up its powder/gas in a shorter amount of barrel so you need to locate the gas port closer to the breech to get enough to cycle the weapon. I am big on having parts on hand to keep my firearms working and if these of common parts, all the better. That said, I would rather have to only stock a different gas tube rather than a lighter bolt/buffer/and or recoil spring. YMMV

[techo]

Is the bore & chamber chromed ? HP tested? Semi or FA carrier included? Shot peened & MP inspected bolt?
The website doesn't list complete specs.

[SomeOtherGuy]

Is the bore & chamber chromed ? HP tested? Semi or FA carrier included? Shot peened & MP inspected bolt?
The website doesn't list complete specs.

Here's what I've distilled from a post here, Rob's "Chart," and some of my own investigation including a contact to AIM Surplus which has these for sale:
-the barrel is WASP treated inside and out. This is a nitriding / nitrocarburizing process. No chrome.
-I would assume not HP tested unless clearly stated somewhere.
-CMMG's standard carrier is in between common semi and full auto styles, with a slight reduction of the lower rear semicircle - it is visually different from an auto carrier and I assume, but don't know, that it's incompatible with an auto sear.
-Per the Chart, for their 5.56 rifles, the bolt is 9310 steel and is neither shot peened nor MP inspected. I don't know for sure that this is true of the 300 Blackout upper, but it would be my assumption.

[Tokarev]

I decided to take a gamble and placed an order for the complete upper (minus handguard, cap and delta ring) this morning. My plan is to install something like a Samson Evo handguard and I didn't see much point in paying an additional $25 or so for plastic handguards that would probably go in the trash. Come to think of it, I should have left off the A2 flash hider as well...

Anyway, I assume I've used CMMG parts and whatnot over the years but this is the first time dealing with the company directly. The gentleman I spoke with was friendly and helpful and was more than happy to work up a price for me as outlined above. He told me that they're running about two or three weeks behind on most orders.

I have no illusions about MP testing of the bolt etc but decided to go this route for my first experience with the .300BLK. If the cartridge proves to be as wonderful as everyone's saying, I'll probably peddle the CMMG upper over on TOS and get myself something from AAC or Noveske.

[SomeOtherGuy]

Very interesting - please post a review when you get it, if you don't mind. I'm also looking for ways to try out this cartridge without dropping $1000+ on an AAC or Noveske upper. Still debating the CMMG but I also see some reasonable prices on stripped barrels at various places, and I may just build an upper since I have most of the other parts lying around. Midway has an "AR Stoner" 16" carbine gas stainless barrel for $220 that has 3 good reviews; they also offer the CMMG stripped barrel for $200 and some other brand for a bit less. Delta Company Arms has higher end barrels for around $300 but I'm not sure on the timeline with them.

[Tokarev]

I've been poking around on various sites for the last few weeks trying to decide which route to take. This seems to be the simplest option. That is if they actually get the product to me in a reasonable timeframe.

I'll be happy to post some updates when available. I assume the upper will shoot okay but I'm curious about overall reliability with sub- and supersonic ammo.

At least this'll give me something to play with while I wait for my suppressor's tax stamp...


EDIT: Just adding up the parts on Midway, I'm looking at $530 or so for pretty much the same stuff before shipping.

[Combat Plastic]

I built a 300 BLK upper using a CMMG M4 style barrel with carbine length gas, CMT upper receiver, Daniel Defense BCG (MPI), and H buffer. The barrel is the WASP (Melonite) finish inside and out. It has been perfectly reliable and with 1.75" groups at 50 yards (only had iron sights at the time). I've only fired Hornady 300 Whisper 110gr. V-Max through it so far. More testing to come with a RDS and various reloads.

[Tokarev]

I built a 300 BLK upper using a CMMG M4 style barrel with carbine length gas, CMT upper receiver, Daniel Defense BCG (MPI), and H buffer. The barrel is the WASP (Melonite) finish inside and out. It has been perfectly reliable and with 1.75" groups at 50 yards (only had iron sights at the time). I've only fired Hornady 300 Whisper 110gr. V-Max through it so far. More testing to come with a RDS and various reloads.

Please keep us posted. Hopefully you'll have no stabilization problems with heavy bullets.

[SomeOtherGuy]

EDIT: Just adding up the parts on Midway, I'm looking at $530 or so for pretty much the same stuff before shipping.

That sounds right if you have no existing parts bin and want to build the exact same design. I'm just looking at building with a SS barrel and some sort of free float forend, with lower incremental cost since my parts bin has a BCG, stripped upper, charging handle etc. The final cost of what I'm planning would be more than $530 when you add the value of parts I have on hand.

I believe that CMMG is the only company at the moment offering an upper or barrel with a pinned A2 style sight base gas block, so if you want that then CMMG is probably the way to go.

[Tokarev]

Model 1 Sales shows a fixed front sight post barrel on their website.

I ordered a lo-pro gas block. I basically ordered the CMMG railed model without their rail. It might be a decent product (never seen one other than on their website) but I don't care for it aesthetically.

[Tokarev]

I've found a little feedback on the CMMG upper over on silencertalk. I see favorable reviews over there. CMMG says they use both pistol and carbine length systems and recommend the carbine length for supersonic. Supersonic should work in the pistol system but they say the gas port's probably a little too big for optimal performance.

In looking at CMMG's chart, the pistol length gas system is best suited for subsonic unsuppressed. I don't see much reason to shoot the subsonic stuff without a suppressor.
http://cmmginc.secure-mall.com/shop/images/M300-AAC-Blackout-Upper-w-Mid-Length-4-Rail-FFT1711-2931.jpg

[SomeOtherGuy]

I don't see much reason to shoot the subsonic stuff without a suppressor.

Although not ideal, the subsonic stuff is surprisingly quiet even without a suppressor, in a 9" barrel upper I shot a few weeks ago. Very low on my personal priority list though - like you I'm looking at this primarily for supersonic loads.

[QuietShootr]

Anyone get one of the 8.5" barrels yet?

[dmaxfireman]

I have one of their 16" uppers I have yet to fire. Once I take it to the range I will post back with results.