20" CMMG AR-15 upper receiver questions

[MMcfpd]

Under consideration at present is the possibility of putting together a 20" AR and I find I'm most strongly drawn to CMMG's offerings, but I have some questions:

• They offer it standard with a shrouded pin semi-auto bolt carrier, but the full auto carrier is a no cost upgrade. From what I've read opinions seem to hold that the slightly heavier FA bolt carrier helps temper the cyclic rate somewhat. First, is that correct? And then, is there any reason not to get the FA bolt carrier?

• Is there any reason to take the polished extended ramps option for $10, or really, is there any reason not to?

This rifle will be using a full set of Ironwood Designs walnut furniture including an A1 style triangular handguard.

• The upper is offered as both a government profile and a medium contour - is one of those better suited to using the A1 style handguard?

• Are there any other problems one might anticipate with using the A1 style handguard? I have found a triangular endcap that fits.

• Is there any downside to getting the A1 flash hider as opposed to the A2 style?

Is there anything else I ought to consider?

Thanks for your help.

 

[Onmilo]

1. In my home state using a full auto bolt carrier can cause some issues with overzealous members of the law enforcement community.
If you are in a more liberal state by all means use a full auto carrier, I use the shrouded pin AR carriers here in blagoland.

2. No reason for them in a 20" rifle but if you want the ramps, ten bucks is cheap enough.

3. Be careful with wood on these rifles. Most current weapon grade walnut wood isn't great quality and is prone to cracking if used in applications where the wood is thin such as AR handguards and AR stocks where the wood is very thin around the extension tube.

4. For general shooting I like the Government profile barrels.
They are thinner, lighter, and the rifle seems to swing on target and respond better in the hands than a medium or heavy barrel.
There is no appreciable accuracy difference until you get out past 400 meters and most people do not shoot at these longer distances.

5. I prefer round handguards, always have, that is just me.
Bust a triangular hanguard side and you have to find a replacement for that side, they don't interchange.
Round guards are easier to hold in most peoples hands and not as slick.
20" barrel long handguards require a triangular endcap be they round or triangular.
Short handguards are designed to work with the round endcap.

6. An A2 flash hider is designed to prevent dust signature when shooting prone and is supposed to act like a muzzle brake.
Apples to oranges an A1 flash hider does just about as well.
The real difference between the two is the original A1 flash hider was designed to fit a smaller diameter barrel than the A2.
My personal preference is the Yankee Hill Phantom flash hider and many shooters like the Smith Enterprise Vortex.

If you don't like the standard fixed A2 buttstock or it is too long I would recommend a MagPul CRT collapser stock or a MagPul Precision Rifle Stock.
Both are expensive, well made and well worth the money.

I like Rock River two stage triggers/hammer assemblies.

Flat tops seem to be more quickly resellable over fixed carry handle uppers.

Get a chrome lined barrel. HTH

 

[Zach S]

No reason not to use a FA BCG.

All CMMG uppers come with M4 ramps. Extended ramps are deeper than M4 ramps are not anodized.

I own a 16" MedCon upper, and am thinking about having it turned down a little. While lighter than an HBAR, there is still a noticeable difference in it and a GI profile. There of course will be a bigger difference in a 20"

A1 HGs are pretty. Otherwise, I dont like them for reasons that Onmilo posted.

CMMG advertises their buffertubes (for six postion stocks) as mil-spec, but mine is not. It has the mil-spec diameter, and mil-spec threads, however the end of it looks like a commercial stock, which is just a tad longer than a mil-spec bufftertube. Now they're listed as 5 position stocks, so they may have the flat end on a shorter tube now.

 

[DMK]

This rifle will be using a full set of Ironwood Designs walnut furniture including an A1 style triangular handguard.

• The upper is offered as both a government profile and a medium contour - is one of those better suited to using the A1 style handguard?

Their 20" lightweight would be most appropriate for A1 furniture.

http://cmmginc.secure-mall.com/shop/?shop=1&cart=815537&cat=61&