Want to build my first AR-15 and have been planning on a longer range gun, so was planning on a 24" bull barrel.   However, today another shooter told me that the performance on a 1x8 24" would be crap unless I was shooting the higher velocity Target/Varmint ammo.

Not sure I want to always have to shoot the higher priced spread.

Opinions?

Mark

I"d say that guy is an idiot.

Quoted: I"d say that guy is an idiot.

+1

Quoted: Quoted: I"d say that guy is an idiot. +1

+2

Quoted: I"d say that guy is an idiot.

+1

What do you want the rifle for?  Hunting? plinking? matches?

IMO there isn't a whole lot of difference between the 20 inch and 24 inch barrel, performance wise.  With the 1x8 twist, your twist is going to shine using heavier match bullets, not light varmit bullets.

It all depends on what you will use this rifle for the most.

Hmm, first double post (see below)

Quoted: However, today another shooter told me that the performance on a 1x8 24" would be crap unless I was shooting the higher velocity Target/Varmint ammo.

Quoth the Oracle:

Q. What twist rate do I want for my rifle? Probably 1:9, but it depends on what kind of bullets you intend to shoot. Special purpose rifles often have uncommon twist rates.  For example, if you are building a varmint rifle and want to shoot the short 35 grain, 40 grain, and 50 grain bullets, a 1:12, or even 1:14 twist would be best.  On the other hand, long range High Power shooters often select 1:8, 1:7.7, 1:7, or 1:6.5-twist barrels to stabilize the long 77, 80 and even 90 grain bullets used for 1,000 yard competition.  Additionally, new testing of heavier rounds (68-77 grains) seems to show that they perform very well in simulated tissue and may be a better defensive choice than 55 grain or 62 grain rounds. The majority of shooters, though, typically shoot bullets of 50 to 69 grains in weight (note that the 62gr SS-109/M855 bullet is as long as a 71 grain lead core bullet) and should select 1:9 twist barrels.  At typical .223 velocities, a 1:9 twist will stabilize bullet lengths equivalent to lead-core bullets of 40 to 73 grains in weight. 1:12 twist rifles cannot stabilize SS-109/M855 bullets and 1:7 twist rifles are slightly less accurate with lighter bullets and will often blow apart the thin jackets of lightweight varmint bullets.  The 1:7 twist is used by the military to stabilize the super-long L-110/M856 tracer bullet out to 800 yards, but unless your plans include shooting a significant amount of M856, the 1:9 twist rate is better suited for general use. There is, of course, an exception: if you want to use loads utilizing the heavier, 75-77 grain match bullets currently used by Spec-Ops troops and other selected shooters, you'll want a 1:7 twist barrel.  Although military loadings using these bullets are expensive and hard to get, some persistent folks have managed to obtain a supply, and will need the proper barrel twist to use them.  Anyone who foresees a need to shoot this ammo should consider a 1:7 twist barrel.

In summation:  The tighter twist is needed for longer bullets (M855/6 and heavier/longer), doesn't hurt 55 grain M193, but will tear the shit out of lighter/shorter varmint rounds.

ETA: It seems odd (to me, at least) that your buddy would group "Target/Varmint ammo" together, as they are decidedly different (longer/heavier vs. shorter/lighter, respectively).

When I built my first AR, I wanted a long range (400+) varmint gun. I went with a M1Sales upper.
Model 1 24" Tac Upper

In hindsight, it is really long and really heavy. My question to the board is, do you really get an advantage at long range with the 24" barrel?
You might be better off with  20" just for practicality reasons.

It really depends what you're gonna use it for.

My 24 " RRA Varmint is pretty heavy, but it's excellent for P-dogs.

<---look left, 69gr BTHP @ 100 Yds (I ran out of range)

OK, thanks for the info.  This guy is a really good IPSC shooter, and has about 4-5 variations on M-15 from 24" on down.

I was getting panicy, thinking that maybe I should buil a "Room Sweeper" short gun first.  But I will not order until the first of the week now.

Another point - some of the guys I consulted early in this decision process were members of the USAMU High Power Team (several past National Champions), and several members of the USAMU reloading section that develop ammunition for HP shooting, and Army Sniper systems.  

These guys did not warn me off of a longer barrel, but when I worried about the twist rate, I was told unless you are going to hand load and tune for ultimate accuracy,
quote "it is hard to over spin most M-16 ammo"  Just a thought

After hearing you guys, I will go ahead with the 24" (Fluted) barrel, but change to 1:9 as a middle ground.

By the way - someone asked what I want it for:  Basically longer range plinking.  I don't hunt, game or varmint.  But the former competitive shooter in me wants to shoot out past 100yds.   I want a gun reasonably accurate out to 400yds with commenly available ammo - 2 MOA with bulk ammo (not total crap).  2 MOA seems easy, without  handloading or buying premium ammo.  Walmart bulk or whatever.

Thanks all.  
Mark