Colt AR15 Question

J

JasonLane

New member
I have a Colt AR15 and was wanting to buy a new upper and barrel. My question is will any brand upper fit my colt lower? Reason I ask is that I heard that they have a slight size difference in the holes where the upper and lower connects. I am wanting to go to a flat top upper with a 20 inch barrel. Right now I have a 16 inch barrel and upper with the agrivating carrying handle. After putting a scope on that everything is thrown out of wack for lack of better words.

Also what kind of twist is good for shots up to about 400 yards? My barrel I have now has 1/7 stamped on it. Is that the twist for it?
 
Sorry I forgot to tell the caliber. It is a 223. After reading some on the 204 I am almost interested in one of them. Who all carries to 204 uppers and barrels?
 
It's easy to determine whether it's a "small pin" lower (which any upper you buy, that's not made specifically for Colt) will fit. If the front pivot pin diameter is .250, you're good to go right now with any upper. If the pin is .312, you'll need an "offset pin adapter" to make them mate up.

You can get one right here for $5, so it's no big deal.

Offset pivot pin

If you want to adapt a big-pin upper to a small-pim lower, get this:

Offset pivot bushing

Quote:Also what kind of twist is good for shots up to about 400 yards?

Anything faster than 1:12 (like 1:10, 1:9, 1:8) will stabilize a heavy enough bullet to shoot out beyond 400 yards. 1:7 is good. 1:7 is so fast a twist, you're getting into the area where you may actually spin the light, thin-jacketed bullets apart, though. If you have a choice, go 1:8, that's a very good compromise between light and heavy bullets.

Quote:My barrel I have now has 1/7 stamped on it. Is that the twist for it?

Yes, one complete bullet rotation every 7 inches of travel.
 
Jason, Your twist rate is used to determine what length of bullet, rather than distance of potential shot the rifle will generally handle well...

I have a .223 that has a 1/14 twist that is dynamite with 40-55gr bullets, another with a 1/12 twist that shoots 40-60gr bullets, and a 1/9 twist that shoots 50-70gr bullets exceptionally well...each heavier weight bullet is a little longer than the lighter ones....All are capable of shooting 400 yards, with reasonable accuracy..

The slow twist barrel (1/14) allows me to push the speed of the lighter bullets a little faster for a flatter trajectory, where the faster twists require a longer/heavier bullet and slower speeds..

If you decide to pick up an AR upper in .204, you will find that the general twist rate is 1/12 and you will want to keep the barrel length at 22", minimum, to realize the optimal potential of the round....most will be 24"...some are made shorter, but you lose some of the velocity potential that really makes the .204 shine...

I used to have a M4 Carbine with a 1/7 barrel and never did find a load that it liked until I got into the 75gr bullets, but then the length was too long to function in the AR magazine..I suspect there was a problem with the barrel to begin with..
 
Thanks OT.

I also have a question about the carrying handle. That is where I have been mounting my scope when I have used it. Just how bad will that affect the accuracy? It puts the scope a great distance away from the barrel so it cant be good right?
 


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