is 18" better than 20" for ar-15?


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futureranger
October 24, 2008, 02:46 PM
I am planning on buying a cmmg ar 15 this summer, i want something I could find more useful than just target shooting but I want it to be able to perform out to 300m. what im trying to ask is, I am on a shooting team at my college and I want a ar15 I can practice with on my own. I was looking at both the 18” 20” med barreled versions, and I want something to fill the gap between my 308 and ak but I would also like it to be a descent target rifle. Is the 18” any better than 20” and vice versa, the 18” is 1/8 twist and 20” is 1/7. Any suggestions are welcome; also I’m in college with only a little spare cash so don’t tell me to buy a night force topped Barrett ;) thanks again

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rcmodel
October 24, 2008, 02:53 PM
If you want a rifle to practice for your ROTC shooting team, it would seem to me you want a 20" AR-15 rifle.

That would give you the same sights, sight radius, and sight adjustment as the GI M-16 rifle.

The only advantage to an 18" is a shorter non-standard barrel length that is neither fish or fowl.
Too short to be a 20" M-16, and too long to be a 14.4" M-4.

With velocity & performance that are different then either.

rcmodel

RockyMtnTactical
October 24, 2008, 03:14 PM
I like the 18" better for practical reasons, and it is a length often used by US snipers, but for target shooting, I don't think it's any better.

I do like the 1/8 twist rate better than 1/7 as well.

ArmedBear
October 24, 2008, 03:16 PM
Rule of thumb: if you're on a budget, go with standard equipment.

Dr. Tad Hussein Winslow
October 24, 2008, 03:20 PM
Rule of thumb: if you're on a budget, go with standard equipment.

I like that. :) The 20" has less muzzle blast and give more velocity.

futureranger
October 24, 2008, 04:04 PM
hey thanks for the advice, if i was later down the road (if it’s still legal then) to put a suppressor on it would the shorter 2” help maneuverability much?

RockyMtnTactical
October 24, 2008, 05:02 PM
Yes, 2" can make a big difference.

Justin
October 24, 2008, 05:25 PM
I can consistently hit steel popper targets at 425 yards with a 16-inch barreled AR, and have pushed the same gun out to about 500, though that hit took multiple shots.

Unless you're competing in High Power matches, barrel length isn't all that important for accuracy.

If you are shooting High Power, then you're pretty much limited to a 20-inch barrel in Service Rifle. I don't recall what the barrel length limitation is for National Match rifle.

futureranger
October 24, 2008, 10:40 PM
Thanks guys, i will just be practicing with the rifle not actually competing so making all the rules isn’t a very big deal, can a 1/8 twist barrel accurately stabilize just about any bullet weight? Or more so than a 1/7?

SimpleIsGood229
October 25, 2008, 01:44 AM
Generally speaking, 1/7 is only necessary if you plan on shooting 75-77 gr. rounds or M856 tracers. Otherwise, 1/9 is just fine.

RyanM
October 25, 2008, 02:03 AM
hey thanks for the advice, if i was later down the road (if it’s still legal then) to put a suppressor on it would the shorter 2” help maneuverability much?

Given that rifle cans tend to be about 8" to 10" long, I'm not sure 2" would make a big difference, there.

Personally, my planned suppressed AR-15 project (c'mon, McCain!) is definitely going to be .300 Whisper, and will probably have a 7.5" or so barrel and pistol gas system. That way, it'd only be about as long as a regular 16", with the can attached. And 7.5" should be enough to get 240 gr up to 1050 fps with a max handload, or 125 gr at 2,100 or so, on par with a krink.

I'd stay away from barrel lengths that don't have a gas system length made specifically for them. 18" is too long for a midlength, too short for a rifle. Tweaking the gas port size can make the gun run okay, but it's still not going to be as reliable as a 20" rifle or 16" midlength.

dscottw88
October 25, 2008, 02:18 AM
The 18 would be my choice over the 20 for all practical purposes. 2" will significantly shorten the overall length and only cause a minimal drop in velocity.

Even better is the 16. The 16 is about as much rifle as you need.

futureranger
October 25, 2008, 04:05 PM
thanks, another thing i was wondering was cmmg also offers a stainless steel barrel for only 25 dollars more, what are the pros and cons of stainless over regular steel?

RyanM
October 25, 2008, 05:52 PM
Stainless isn't as durable and won't have quite as long a life, especially if you rapid fire a lot. But the bore and chamber dimensions will be more precise than a chrome-lined barrel, which will result in better accuracy during the barrel's service life.

RP88
October 25, 2008, 06:09 PM
SS barrels are more precise and even, and are used for match rifles. Chromed barrels are pretty much going to last forever and be VERY resistant to rust and grime unlike match barrels, but at the cost of 0.25-0.5 MoA accuracy. That's enough to make or break a match for a highly competitive shooter.

ridiculous amounts of Precision? Get stainless.

zombies, jungles, deserts, Wolf ammo, and longer life? Get chrome.

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