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gunsrfun
07-23-2007, 2:36 PM
What is the difference between these 3 CMMG uppers. The 18" M18-M SPR Upper, 18" M18 Rifle Length SPR Upper, and the 18" SPR Upper w/Mid Length Gas uppers. I know the rifle length has a fill legnth gas sytem, but I couldn't finds any other difference. If it matters I am building up a SPR type rifle.

proraptor
07-23-2007, 2:43 PM
The last one has a midlength gas...I think the first one is medcon contour

bwiese
07-23-2007, 2:56 PM
I believe CMMG's 18" SPR barrel comes in only one taper/profile.

However, you can get the bbl with the front sight block in various positions, and with gas block in separate position if you want - of course gas block can't be forward of front sight block :)

I STRONGLY recommend you don't get rifle length gas tap (regardless of where the front sight block is). I always like an appreciable amount of barrel ahead of my gas tap, and personally think the middy gas tap is ideal.

CMMGs model designators/ad copy aren't too clear so call 'em up and ask for the exact combo you want.

NRAhighpowershooter
07-23-2007, 3:28 PM
I have the 18" middy and the barrel is a heavy barrel profile.. I DO love it better than my 20" Govt profile blaster rifle....
http://www.imagestation.com/picture/sraid225/p4bc2335977acf34dcc134da8b47ed42c/e87245c5.jpg

unimog_88
07-23-2007, 7:03 PM
CMMG has three configurations for 18" BBLs. The profiles are identical. They are all med-contoured.

#1: Gas port at mid-length, FSB at mid-length.
#2: Gas port at mid-length, FSB at rifle-length, with low-profile gas block.
#3: Gas port at rifle-length, FSB at rifle-length.

That's all I know.:)

caduckgunner
07-23-2007, 9:14 PM
#2: Gas port at mid-length, FSB at rifle-length, with low-profile gas block.

That's all I know.:)

Is there a use for this, or is it just for looks?

bwiese
07-23-2007, 9:47 PM
: Gas port at mid-length, FSB at rifle-length, with low-profile gas block.

Is there a use for this, or is it just for looks?


Absolutely. IMHO it's preferred.... hell, it's the one I chose. You want the middy gas port but you get the rifle position front sight for extended sight radius (kinda like Bushmaster Dissipator configuration).

You don't want a shorter bbl with rifle gas tap and not much bbl in front of it.

Lotsa turkeys cut down 20" bbls to shorter bbls and wonder why their ARs start having problems - the gas tap has to be moved. Some folks convince these cutdown-bbl-w/rifle-gas-tap setups to work but they have to open the gas port wide enough that cycling is very harsh/rough.