Building an AR-15, need advice


November 10, 2008, 11:07 AM
I'm working on an AR-15 and I need a little advice on the lower parts and the barrel.

First of all, I have a CMMG receiver. I plan on getting a CMMG upper to go with it, and I want to have a very basic M4 style configuration. I've decided that I want to go with the 14.5" barrel with a pinned phantom flash hider, bringing the OAL to 16". I don't want to argue about that, so let's stay on topic.

Now it is my understanding, which could very well be wrong, that the military M4s have 1:7 twist barrels, and the 20" M16s have 1:9 twist. It is my understanding that 16"-20" should have the 1:9 and <16" should have a 1:7. I don't know if I am way off on this or not, since I don't know much about twist, in fact it's probably not even called twist, so you get the idea of how "vast" my understanding is.

Anyway, I will be using the rifle for home defense/SHTF, not for hunting or extreme marksmanship. I expect the rifle to be able to hit a target relatively easily out to 300+ yards. I will not be using super-awesome-elite-tactical-high-performance-kick-ass ammo, and will be sticking to cheap milsurp stuff (brass cased, not wolf). I will probably find one cheap milsurp cartridge and only ever buy that kind, so "variety of ammo" is not really a big deal. Probably some S&B or something.

So with all of those factors, what can you tell me about the barrel twist? Should I be going with a 1:9 twist, or going with a 1:7? Or, if you really want to be super-awesome, which bullet weights would be optimal for both twist rates (specific to the 14.5" barrel, please)?

Sorry to be so specific, but I have been searching all over the web and for some reason I can't find the answers to my question.

Next question.... I was thinking about sticking to CMMG for all of my parts, but I noticed that the DPMS lower receiver parts kit (trigger, hammer, springs, grip, etc.) is a bit cheaper and more readily available. Is the DPMS any good? Is the CMMG better? Is there one I should be considering instead, that's in the same price range ($50-70)?

And lastly, I am getting a quad rail system for the rifle, but I don't want to spend a fortune. I was thinking about getting a UTG quad for about $55. From the reviews I've read, it's really sturdy and everyone seems to love it. I think that for my budget (I have M4 taste and AK money... make that SKS money), it's probably the best I'm going to get. Since I'm not planning on putting any optics or lasers on it, just a flashlight and maybe a vertical grip, is this the best value for my money? Is there anything else that's competitively priced that I should be considering? I really don't want to spend more than $75 or so, and I definitely don't want anything that isn't drop in (so no free-floating one-piece deals). Simple is better for me. So is cheap.

Thank you all for looking and for any advice you might have. I appreciate it greatly.

BTW, Magpul P-Mags... Love 'em? Hate 'em? Anything I should be aware of?

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November 10, 2008, 11:38 AM
I'm pretty sure your theory on twist is incorrect, and that all .mil rifles use 1-7" twists. 1-9" is purely commercial.

Unless you plan on shooting 70+ gr ammo, you don't really need a 1-7". That being said, I have a 1-7" M4 style upper and I'm not sure if I will ever need to shoot super heavy bullets, but it will still run 55 grainers well.

As far as parts kits go, I wouldn't stress too much on what the brand name is. They all come from .gov contractors so they should be pretty close to the same.

November 10, 2008, 11:42 AM
Search on twist - there are a lot of threads. Barrel length is not the issue - bullet length (and therefore, partially, weight) is what matters. For general run of the mill ammo, you're going to be shooting 55gr - 62gr - 1:9 is fine, 1:8 would extend the utility a little to 69-75 gr heads. That's 'on average' - lots of 1:9s shoot 77gr Sierras acceptably out to 300 while some 1:7s will handle 55s - but in general, stay between 55 and 69 and you're fine w a 1:9.

DPMS LPKs are fine BUT, count all the parts the minute you get it ... they have a habit of skipping a pin or 2 in packaging.

No idea re rails - I only shoot full length SRs.

November 10, 2008, 12:19 PM
Thank you for the replies!

So if I was going to get this ( 55grn ammo, a 1:9 twist 14.5" would be better? Or does it really even matter at all? BTW, the ammo claims to be .223, but I'm pretty sure it's actually 5.56. I could be wrong, I read it somewhere.

November 10, 2008, 12:25 PM
All Military barrels are 1-7 twist. 1-9 is fine for 55-62gr. My 1-7 shoots everything fine.

November 10, 2008, 05:24 PM
1x9 or 1x7 both fine, but i'd go with the 1x9. no major difference if using for home D. the 1x7 twist is also used for firing tracer rounds. 55gr is perfect for 1x9 twist and is pretty common. Also, colt originally wanted to change their guns to 1x9 but DoD didn't want to because 1x7 was "nato standard"

make sure your barrel is 5.56NATO. a 5.56nato barrel can fire .223, but a .223 can't handle 5.56 and isn't recommended using 5.56 in a .223.

Sellier & bellot, federal, american eagle, winchester all good ammo and probably the cheapest after Wolf. (id never use wolf)

as for pmags, they are hands down the Best mags money can ever buy period. USGI mags are fine, but a magpul pmag is nearly indestructible, always feeds, always reliable.

If you enjoyed reading about "Building an AR-15, need advice" here in archive, you'll LOVE our community. Come join today for the full version!