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mywytefeet
12-14-2008, 6:41 PM
So I am going to build my first AR-15 and have a few questions pertaining to CMMG uppers. I looked on CMMG's website and am looking for a 16" barrel, 1/7 twist, mid length, upper. My question is, what is the difference between SKU Number: U-1605 upper

[New 16 mid-length upper. This upper comes with mid-length handguards and is complete with bolt, carrier and charging handle. CMMG semi auto bolt carriers have the shrouded firing pin to protect against hammer wear. Upper receivers are T marked and include extended feed ramp cuts. Features include gov’t contour barrel, 11 degree recessed target crown, mid-length gas system, chrome lined 5.56mm chamber and bore, 1/7 twist, parkerizing under “F” marked forged front sight base and magnetic particle testing on every barrel. When ordering with optional gas block, barrels will not be drilled for taper pins. Barrel is marked CMMG MPC 5.56 NATO 1/7.]

and SKU Number: U-1605L7

[New 16 lightweight mid-length upper. This upper is complete with bolt, carrier and charging handle. CMMG semi auto bolt carriers have the shrouded firing pin to protect against hammer wear. Upper receivers are T marked and include extended feed ramp cuts. Features include lightweight profile mid-length barrel with 11 degree recessed target crown, chrome lined 5.56mm chamber and bore, 1/7 twist, parkerizing under .625 diamter "F" marked forged front sight base and magnetic particle testing on every barrel. When ordering with optional gas block, barrels will not be drilled for taper pins. Barrel is marked CMMG MPC 5.56 NATO 1/7.] ?

I also have a few basic questions as:

What is CAR gas? such as the CMMG M10 MedCon upper? SKU Number: U-1604M

Also, are M4 uppers just made to attach grenade launchers (that I'll never own) or is there something else to them? such as CMMG M4 A1 SOCOM Upper SKU Number: U-1604A1 and CMMG M4 Upper SKU Number: U-1604.

and finally,

out of all the models listed:
SKU Number: U-1605 Mid-Length Upper
SKU Number: U-1605L7 Lightweight Mid-length Upper
SKU Number: U-1604M M10 MedCon Upper
SKU Number: U-1604A1 M4 A1 SOCOM Upper
SKU Number: U-1604 M4 Upper

which would you recommend and why?


Thanks so much!

TurboFall
12-14-2008, 6:50 PM
16" lightweight means the barrel profile is very thin: less weight, accuracy may decrease faster due to a warm barrel. The non-lightweight handles heat better, but weighs a bit more.

If the M4 upper has the M203 cut, it's to support the grenade launcher. No use to civilians other than looks.

CAR gas means carbine-length gas system. People claim midlength gas systems are more reliable, softer recoil; but keep in mind the US military as well as many civilians haven't had a single problem with a carbine gas system.

As for uppers, be a man. Go with a 20" :p

Bimmer2
12-14-2008, 6:53 PM
I've got a CMMG mid-length, lightweight.

The difference between the first two items is that one is a lightweight barrel, the other is middle weight.

You don't want a CAR-length gas system. You want a mid-length.

Yes, the "M4" barrel with the step is just to look "tacticool." If you're getting a mid-length, then you're not getting an M4, anyway.

mywytefeet
12-14-2008, 6:54 PM
16" lightweight means the barrel profile is very thin: less weight, accuracy may decrease faster due to a warm barrel. The non-lightweight handles heat better, but weighs a bit more.

If the M4 upper has the M203 cut, it's to support the grenade launcher. No use to civilians other than looks.

CAR gas means carbine-length gas system. People claim midlength gas systems are more reliable, softer recoil; but keep in mind the US military as well as many civilians haven't had a single problem with a carbine gas system.

As for uppers, be a man. Go with a 20" :p

Thanks very much! Helps with narrowing what upper I want.

mywytefeet
12-14-2008, 6:55 PM
I've got a CMMG mid-length, lightweight.

The difference between the first two items is that one is a lightweight barrel, the other is middle weight.

You don't want a CAR-length gas system. You want a mid-length.

Yes, the "M4" barrel with the step is just to look "tacticool." If you're getting a mid-length, then you're not getting an M4, anyway.

Oh, I see. Thanks! Based on the models listed, I think I will go with the U-1605 Mid length Upper.

Thanks!

Bimmer2
12-14-2008, 7:04 PM
... but keep in mind the US military as well as many civilians haven't had a single problem with a carbine gas system.

Sorry, but AFAIK this is just flat wrong. I'm not trolling for an argument here, but it's pretty clear that there are reliability and durability problems with the carbine-length gas system, especially with a 16" barrel.

Poke around on M4C.net.

TurboFall
12-14-2008, 7:21 PM
Sorry, but AFAIK this is just flat wrong. I'm not trolling for an argument here, but it's pretty clear that there are reliability and durability problems with the carbine-length gas system, especially with a 16" barrel.

Poke around on M4C.net.

Not trying to incite anything, but I'd much rather trust the millions of carbine-length gas systems still in circulation than the claims of a website. If there was anything significantly wrong with a carbine-length gas system, we'd be seeing manufacturers (especially the top-ends) changing to midlengths; they haven't.

ocg 03
12-14-2008, 8:19 PM
I agree. I just got an LMT M4 Upper... and if it's good enough for the military, it's good enough for me.

Dragon
12-14-2008, 8:44 PM
Never had a problem with my M4 ! Clean an oil,oil,oil your rifle!

Bimmer2
12-14-2008, 8:57 PM
OK. I'm not trying to bash the M4, and they seem to work well with extra-powerful extractors and heavier buffers, but those just treat the symptoms. The real problem is that there's simply too much gas pressure, too early.

Using a civilian 16" barrel instead of a mil-spec 14.5" barrel just makes it worse.

As for the "top-ends:" LMT and Noveske both make mid-lengths. Colt is about the only manufacturer that doesn't, but they've already rolled out a piston upper — the booming business in piston uppers should be a clear sign that there's something wrong with the design.

aplinker
12-15-2008, 12:44 AM
Not trying to incite anything, but I'd much rather trust the millions of carbine-length gas systems still in circulation than the claims of a website. If there was anything significantly wrong with a carbine-length gas system, we'd be seeing manufacturers (especially the top-ends) changing to midlengths; they haven't.

Actually, they are. Most of the current trial entries use gas systems that are not DI carbines. Including Colt's.

M4 armorers see about a 30% breakage rate of bolts. M16 armorers see a few in their career.

The military makes choices and sticks with it. It's not always the "best." Further, most commercial carbines aren't even on par with Colt, so you're even better off with a mid-length there.

16" lightweight means the barrel profile is very thin: less weight, accuracy may decrease faster due to a warm barrel. The non-lightweight handles heat better, but weighs a bit more.

If the M4 upper has the M203 cut, it's to support the grenade launcher. No use to civilians other than looks.

CAR gas means carbine-length gas system. People claim midlength gas systems are more reliable, softer recoil; but keep in mind the US military as well as many civilians haven't had a single problem with a carbine gas system.

As for uppers, be a man. Go with a 20" :p


Are you just making guesses here? Why don't you let people who understand barrel profiles answer rather than confusing people.

SKU Number: U-1605 Mid-Length Upper
Government profile (thin under handguards and thicker at the gas block) with mid-length gas
SKU Number: U-1605L7 Lightweight Mid-length Upper
this contour is the same thickness throughout, but essentially splits the difference between the thick and thin part on the gov't. Mid-length gas. An excellent choice for a run & gun rifle
SKU Number: U-1604M M10 MedCon Upper
thicker profile for whole length. Will be stiffer and heavier. Mid-length gas.
SKU Number: U-1604A1 M4 A1 SOCOM Upper
Similar to a medcon, thicker under the handguards than gov't, heavier. Was designed for heavy F/A usage. M203 notch. Carbine gas.
SKU Number: U-1604 M4 Upper
gov't profile with M203 notch. Carbine gas.

To see what each of the barrels actually look like & how they compare, look here:
http://cmmginc.secure-mall.com/shop/?cart=1403440&cat=67&

I'd suggest sticking with a mid-length gas. Pick the profile you like. Heavier is better for a RECCE style (using magnified optics and Mk262 clone ammo) and lightweight is fantastic for a red dot with XM193 or similar.

mywytefeet
12-15-2008, 1:03 AM
Thank you UCLAplinker! VERY INFORMATIVE response! Now I have a much better idea about the profile of upper I want. Also, thanks for the huge newbie ar-15 write-up you did--that's the first thing I read when I wanted to get some basic information--also very helpful!

I am thinking the I might go with the light weight mid length 16" upper. I'd like to have a red dot on it with flip up iron sights as well (the idea of having both options seems best to me.) I'm thinking about getting this along with a red dot. What do you think UCLAplinker?:

http://i3.photobucket.com/albums/y64/mywytefeet/Picture2.png

aplinker
12-15-2008, 1:12 AM
Skip the LMT enhanced bolt/carrier - they're designed for carbines.

Put the money into a better free float rail (like Daniel Defense or LaRue) - the YHM is really thick around.

Consider whether you might prefer a lo-profile build over the flip front sight gas block. I personally like the simplicity of an A2 fixed FSB - it really doesn't interefere with optics, is cheap, doesn't need to be deployed and is bulletproof tough.

I'd probably skip the Vortex Striker, too. How often do you break glass? ;)

mywytefeet
12-15-2008, 1:20 AM
Thanks for the honest opinion plinker! Wasn't sure about the LMT enhanced bolt/carrier--good to know--I'll stick to the standard. I'll also look into a different free float rail (seems like everyone loves LaRue--maybe I'll look into that.) As far as the flip up front sight goes, I really didn't know what to get--my thinking was that anything otherwise would get in the way of optics, but hey, if a fixed A2 FSB doesn't interfere with optics, and saves me money, then I'm happy with that!

As far as the Vortex goes...well...I was just thinking, you know...elephant **** hits the fan...might need to kick *** and bust glass lol =P Guess you're right I probably won't be busting glass =)

At least I have a much better idea of what I want now. Thanks again Plinker!