20'' Barreled AR's..Need some advice

[rdsii64]

Originally Posted by ICANHITHIMMAN

A NM AR barrel is .750 from the gas block forward

You are correct. That was what I meant.

[The7mmSTW]

i think ill be going with a 1 and 7 twist

[7mmSendaro]

I have a 20" Barrel Rock River EOP and it shoots like a dream. It has the 1-8 twist and loves 69 grain SMKs but still shoots 50 grain bt great too. It is a little heavy but shoots well of bags or a bipod.

[Kevin Thomas]

I find it a bit amusing that we're having a discussion/debate about a 20" barrel instead of "the standard 16-inch" tube these days. After all, the 20" barrel WAS the "standard" length for this rifle when it was originally designed, and has remained so until fairly recently. Now, the 14.5" M4 variants have become the standard issue, and the 20" versions are starting to stick out like sore thumbs in a platoon formation. Evolution in action, I guess.

However, let's not forget that there are certain immutable rules of interior ballistics and expansion ratios that dictate there's a price to be paid, performance wise, from a shorter barrel. The 20" will virtually always deliver higher velocities than the shorter barrels,but do so at the expense of slightly more cumbersome handling qualities. Those of us used to the 20" barrels will probably always regard them as the standard, and the shorter guns as being the trade-off versions for better handling in close quarters. Just depends on what you're used to now, I guess. Still, I find it amusing that the typical 18 year old fresh out of BCT probably views a standard 20" M16A2/A4 like it's some sort of Civil War era musket. I can only imagine how they'd look at my 26" Match Rifles built on the AR platform. No particular point here, just think it's funny how things have developed over the years.

[rdsii64]

Originally Posted by Kevin Thomas

I find it a bit amusing that we're having a discussion/debate about a 20" barrel instead of "the standard 16-inch" tube these days. After all, the 20" barrel WAS the "standard" length for this rifle when it was originally designed, and has remained so until fairly recently. Now, the 14.5" M4 variants have become the standard issue, and the 20" versions are starting to stick out like sore thumbs in a platoon formation. Evolution in action, I guess.

However, let's not forget that there are certain immutable rules of interior ballistics and expansion ratios that dictate there's a price to be paid, performance wise, from a shorter barrel. The 20" will virtually always deliver higher velocities than the shorter barrels,but do so at the expense of slightly more cumbersome handling qualities. Those of us used to the 20" barrels will probably always regard them as the standard, and the shorter guns as being the trade-off versions for better handling in close quarters. Just depends on what you're used to now, I guess. Still, I find it amusing that the typical 18 year old fresh out of BCT probably views a standard 20" M16A2/A4 like it's some sort of Civil War era musket. I can only imagine how they'd look at my 26" Match Rifles built on the AR platform. No particular point here, just think it's funny how things have developed over the years.

I can certainly smell you're cooking here. With in the sand box that sane chamber pressures allow me to operate in, I am a speed freak.
To a point, the longer barrel will let me get to faster muzzle velocities and keep the chamber pressure where they should be. A 24 inch 8 twist barrel will launch a 75 grain match bullet a 3000 FPS bellow max safe preasures if you pick your powder wisely.
Since I hunt with my AR15 and tend to keep my shots at 300 and in, a 20" barrel is a good compromise while still letting me cut a few X's from the 600 yard line.

[timmay]

I think the best length barrel for the AR-15 for an all around rifle for hunting and self defense is 18". I personally have a m16A5 clone (A5 meaning if the military decides on the vltor stock for their A5) with a 20" barrel and I absolutely love it.
The special purpose rifle the military uses has an 18" barrel.
I get very good velocity with the 20 inch. Mine has the gov profile barrel from BCM. Its light enough to carry anywhere and still heavy enough for repeated firing.
The 18" isnt going to lose too much velocity and will be a little faster
18" or 20" is the best bet.

[ICANHITHIMMAN]

I rocked a M16A2 on my first tour to Afghanistan I hated it! Mostly do to the CDI factor and that I was allways in little trucks and tight quarters conducting meetings. I upgraded it to a Mk18 after about 2 months in country. It was a much better fit for my mission. In Iraq I got a brand new M4 slaped my ACOG on it loved it!

So having run 3 diffrent barrel lengths for extended tours I have decided I like the 14.5" barrels with long hand rails. I actualy just took my 20" apart putting it back to an A4 and selling the handguard. Just some thoughts