Building my first AR


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STAGE 2
February 26, 2007, 04:01 AM
Since I'm stuck in the PRK I can't buy one of these out right, so I've decided to build one myself.

The final result will be a stock 20" A2 AR15, no aimpoints, no rails, no tacticool junk. That said I have 3 questions.

First, why does the government use a 1:7 twist rate where as most commercial AR's have a 1:9. Which is "better" if there is such a thing and why.

Second, has anyone dealt with CCMG? I've been looking at their lowers and they seem to be decent.

Finally, how much of a weight/balance difference is there between the heavy barrel uppers and the regular government profile barrel. I don't mind weight as my normal shooters are of the wood and steel variety, but if puts the rifle at an awkward balance I probably would rather have the stock barrel. Also, will the heavy barrel last longer than the government barrel.

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funfaler
February 26, 2007, 04:55 AM
The 1:9 twist is for more stability at lighter bullet weights, the 1:7 will allow for weights up to 80+ grain, the former is limited to @65 grains.

@.75 lbs diff between heavy and M4 style. My thoughts is go lighter, or quicker.

The barrel wears from the inside out, so the heavy won't last longer.

No experience with CCMG

Good luck

BamBam-31
February 26, 2007, 05:04 AM
I had a RRA NM heavy barrel 20" upper. VERY nose-heavy (but VERY accurate as well). Sold that, picked up a Colt Vietnam era upper (thinner profile than the government), and the rifle handled infinitely better. Glad I made the switch.

Haven't dealt with CMMG myself, either, but they've been getting good reviews on Calguns.

I always think having a flat top upper is preferable to a fixed A2 carry handle configuration. With the flat top, you can get a detachable CH that works just as well, or you can remove it for optics and a BUIS if you so choose. The flexibility/modularity is what AR's are all about, IMHO.

nico
February 26, 2007, 10:26 AM
the former is limited to @65 grains

That's very debatable. Plenty of people have reported getting fine accuracy with 55gr bullets in a 1:7 barrel. 1:9 is more ideal for that weight, but saying that you can't shoot anything below 65gr in a 1:7 barrel is going too far IMO.

only1asterisk
February 26, 2007, 11:03 AM
CMMG is good to go.

David

DogBonz
February 26, 2007, 11:15 AM
The 1:9 twist is for more stability at lighter bullet weights, the 1:7 will allow for weights up to 80+ grain, the former is limited to @65 grains.


1:9 was the best compromise that could be found. It will shoot a wide variety of weights well. Although it is not “ideal” for anything under 55gr or over 62g, it still will shoot 40-72 gr bullets very well (depending on barrel quality, of course). The Army now uses a 1:7 for two reasons. The first is to shoot heavy bullets in an effort to increase lethality. The other is to make sure that they are imparting enough spin with the 14” barrels of the M4.

shark3-1
February 26, 2007, 12:40 PM
1:7 was adopted to better stabalize M856 tracer rounds. Either twist will work well. I shoot 55gr. Black hills blue box out of all my 1:7 barrels including the 10.5" barrels, no issues with accuracy or stabilization. You will not have any problem with either if you shoot between 50-70gr projectiles. If you want to shoot heavier than 70gr, a 1:7 would be a better match. If you want to shoot less than 50gr, a 1:9 will be a better match. I've heard good things about CMMG, but haven't owned any of their stuff.

Eleven Mike
February 26, 2007, 01:17 PM
Why do you want an AR, are you some kind of terrorist? :p

AndyC
February 26, 2007, 01:46 PM
hehehe...

Eyesac
February 26, 2007, 02:42 PM
What would happen if I shot say a: 77gr bullet out of a 1/9 barrel? Would it just be less stable, tumble at long ranges, be less accurate?

(sorry to ask questions on you thread)

shark3-1
February 26, 2007, 02:56 PM
Eyesac: What would happen if I shot say a: 77gr bullet out of a 1/9 barrel? Would it just be less stable, tumble at long ranges, be less accurate?

(sorry to ask questions on you thread)

Maybe no detrimental effects will occur, or maybe all three things will occur, no two barrels are exactly alike. The odds of the round being properly stabalized will increase if you go to a faster rate (1:8 or 1:7).

STAGE 2
February 26, 2007, 04:54 PM
So if I read this right, 1:7 should allow me to shoot a greater variety of ammo with less ill effects.

shark3-1
February 26, 2007, 05:07 PM
So if I read this right, 1:7 should allow me to shoot a greater variety of ammo with less ill effects.

Unless you plan on shooting lots of 40gr varmit ammo, you will be fine.

RockyMtnTactical
February 26, 2007, 09:23 PM
1:7 was adopted to better stabalize M856 tracer rounds.

+1

I personally tend to like 1/9 the best since they shoot 55gr ammo more accurately than 1/7's and that is what I mostly shoot.

Most people with 1/9's can shoot the super heavy 77gr rounds just fine too.

10-Ring
February 26, 2007, 09:29 PM
Just finished my CMMG 9mm AR and I have 500 rounds through as of last saturday w/o a single hiccup...I like'em ;)
Good luck w/ your build :D

STAGE 2
February 26, 2007, 10:41 PM
Just out of curosity what is the bullet weight used by the military in their M16's and M4's

RobG5538
February 26, 2007, 11:33 PM
I am looking to do the same. Where did you guys buy your parts, specifically the lower?

Not to hi-jack but, is anyone familiar with the RRA complete CAR A4 rifle/upper kit? Seems to be a good deal.




Rob

RockyMtnTactical
February 27, 2007, 12:08 AM
Just out of curosity what is the bullet weight used by the military in their M16's and M4's

62gr M855 in general (for use with 1/7 twist barrels) although I've heard that some units are getting more 55gr M193.

M193 is made to be used specifically with the 1/12 twist barrels that are still out there.

The 77gr Black Hills OTM is getting some usage.

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