what upper to go with?

[esaabye]

Need some opinions…

So I am working on my first build and need help choosing an upper config. I want a 16in flat top setup but the questions are as follows.

1. Carbine or mid-length? Seems to me the mid-length will offer better sight radius when using the iron sights but I assume there is a downside to this configuration else the 16in carbine would not be offered.
2. Barrel twist rate? As I understand it the 1/9 is best with a 62gr, the 1/7 is good up to 75 or so and for 55 or less you are best with a 1/12. With that understanding I do not know why all I see is 1/9 or 1/7 when the only ammo I see is 55gr or lighter varmint loads.
3. Does the front sight get in the way when using a red dot type scope, should I go with a low profile gas block and flip up sight?


Looking forward to your replies, thanks.

[ChadAmberg]

On the twist rate, are you sure that 55grain is best with a 1/12 twist, or is it the other way around, that with a 1/12 twist you're best using only 55grain? My 1/7 twist just loves 55gr.

As for the red dot and the front site post, that depends on lighting and how you use it. If you shoot both eyes open with the red dot, then you shouldn't have any issues at all. If you use a red dot as a scope, carefully aiming, then the lighting will have more to do with it. Generally I don't have a problem when I shoot like a scope either, but there have been times I wish I had flip up front sites. You can also get the 1/3rd co-witness riser for the mount, and you won't have the problem.

Carbine vs mid-length for me is simply portability. If I were going for pure long range shooting, the longer the better. The shorter barrel for me means the gun is a little lighter, better balance, and easier to move around with. It's only a couple inches different though...

[esaabye]

I double checked the twist rates, the M16A2 introduced the 1/7 to deal with the heavy M855 vs the M193 in the M16A1 with a 1/12.

As I understand it the heavy load needs better spin to stabalize, the M855 would start to tumble in the 1/12 at 100 yds.

As far as length, I was speaking of the gas system. You can get a 16 in carbin or mid length (http://www.del-ton.com/AR_15_Barrel_Assembly_p/dt1023.htm)

Seems the weight would be the same or close and the portability and easy of use would be the same.

[mutt]

I'd stay away from a 1/12 barrel. Why limit yourself to 55gr? Both my 1/7 and 1/9 fire 55gr just fine and I have the option to go with m855 or heavier and still have an effective weapon past 100 yards. As for the gas system I've read the mid is technically superior but I've never had a problem with my carbine length rifles. I don't think it's that much of an issue unless you're real picky about how your gas system operates. ar15.com has tons of good info on it.