Cmmg 18"

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Bartkowski

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I realize that there have been lots of threads on AR-15's just recently and from long ago, but my search isn't working and this site is running slow for me now.

I was wondering what everyone thought about the CMMG 18" SPR upper with the mid-length gas system. Is there a point in getting the 18", and how does the mid-length gas system perform? Everything I have heard about and everything I have seen of CMMG's has been good, but I would like more opinions.
 
Alot of people go 18" so they can use the rifle length gas. If I was going 18 (and Imay) I'd do the rifle.
 
cmmg == good value (not the best, but not bad, and fairly cheap)
18" == optimum for the cartridge
middy == decent compromise. (way better than carbine length, but rifle length works great on my 17", so it's not clear to me what there is to gain from the shorter gas system on a longer barrel)
 
I read somewhere that the rifle length gas system would cause problems in the cold, but was never told how cold thats why I thought about going mid-length. Just to make sure, there is nothing wrong with the mid-length and it is preferrable on a 16" barrel, right? You just think that it makes sense to get the rifle-length because the gun would have an 18" barrel.

One reason I like the 18" is because it has a 1/8" twist and I will be shooting a fair amount of lower grade ammo and most of it is 55gr. Does 55gr. shoot decent out of a 1/7, or even a 1/8, or should I just get a 1/9? Sorry about all the questions, I read around but there are so many opinions.
 
bartkowski, you can get any twist on any length barrel.
 
I read somewhere that the rifle length gas system would cause problems in the cold, but was never told how cold thats why I thought about going mid-length.
Click to expand...

The military is using rifle-length gas on their 18" SPR and it is seeing some action in cold, high-altitude areas of Afghanistan with no issues.

Just to make sure, there is nothing wrong with the mid-length and it is preferrable on a 16" barrel, right? You just think that it makes sense to get the rifle-length because the gun would have an 18" barrel.
Click to expand...

Yes. The midlength is ideal on the 16" because it is a good ratio of longer gas tube with decent dwell time. On the 18", you will have a slightly longer than optimum dwell time. A mid 18" will work; but I think the 18" rifle is a better solution (though how much better is up for debate).

1/8 will handle 55gr just fine.
 
Alright, thanks for all of the information. I will look and see if there is anything at the next gun show, hopefully finding some good deals on lowers.
 
gun show is last place i'd look for quality AR parts.
 
I know it isn't the best place, but a new lower is the same at the gun show as it is at a store assuming they are the same make. I will probably end up ordering parts online.
 
The CMMG M18R uppers are 479 shipped.
CMMG stripped lowers 110. LPK 55
CMMG 6-pos with tube, spring, buffer 75
If you cant do better then that at the show drop me a line

I really like the 18 middy and rifle length. Have been handling handloads and M855 surplus great.
Pete
 
How much does the 18" rifle length upper weigh, and how much does the mid-length 16" upper weigh with the m4 profile barrel?
 
Shouldn't matter where you buy parts as long as you can ID the parts and check them out. Several vendors at the gun shows here sell LMT, Colt, and Stag. Lots of cheap crap too.
 
According to the chart of different AR-15's and what options they have, CMMG seems to be lacking lots of the options some consider essential. (the chart wouldn't post, but it is the one with X's blue 1's and red 2's)

Is that chart correct, because they say CMMG offers a properly staked gas key as an option or in limited runs. I don't think that they have that as an option, and don't know how it would be in some rifles, but not others. Either they would do it or not right? And a shot peened bolt, an option? Or is the chart incorrect?

Also, one of the options when looking at uppers, is have polished extended feed ramps or extended polished ramps. When they say extended, do they mean that they are M4 feed ramps and the anodized ones are not?
 
I have also wondered what the difference is between the two options

anodized ramps vs. extended/polished ramps.

The description says "extended feed ramp cuts" so I assume they both are ~M4. Maybe the only difference is that one is anodized and one polished (the extended part is just repetitive).

While we are on the topic of CMMG uppers. Is there any reason not to get the full auto bolt carrier? Does it have a firing pin that is not completely shrouded (or is that part of the bolt....I am a noobie)

EDIT: Found this after a little searching

http://thehighroad.org/showthread.php?t=235572&highlight=CMMG
 
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In the past, some companies (like RRA) cut their own feed ramps after the receiver had been forged and anodized. Some people are concerned about this since it cuts through the protective layer of anodizing on the upper and doesn't look as good usually.

Extended ramps that are anodized are part of the receiver forging. This is what you see on issue M4s.
 
According to the chart of different AR-15's and what options they have, CMMG seems to be lacking lots of the options some consider essential.
Click to expand...

The chart you're referencing is in this thread.

Seems to me that most things listed in the chart as CMMG options are BCG related. Other than the bolt upgrades, they stack up very favorably against the other AR manufacturers. For example, my CMMG barrels were parked under the FSB and MP tested and the proper height, they offered 1:7" twist, their barrels were all chrome-lined, the gas keys on the carrier were staked correctly, their barrels and receivers had M4 feed cuts, the buffer extensions were MilSpec, and so forth.

All in all, I consider CMMG to be a cut above most in terms of features and QC.
 
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