I'm planning a new rifle build and I'm now trying to decide which is best. The 16" or 20"

Either way, the barrel will be free floated, flattop, and toped with a 1-4x scope. No irons.

I'm just curious if accuracy differences are great between the two, especially with a FF barrel. I have heard supposedly that little accuracy is gained over even a14.5" M4 barrel, but I trust the advice of my fellow ARFCOM'ers more.

As you know, accuracy is 1/3 barrel, 1/3 ammo, and 1/3 shooter.

As to the barrel factor, I can't speak from personal experience, but I do know that the longer the barrel, the greater the muzzle velocity (MV), which can make a difference at longer ranges, say at 200 yds and beyond, because there will be less bullet drop and better crosswind resistance if the bullet has greater MV to begin with.

Remington's ballistics info says they estimate about 30 fps difference per inch of barrel length for ammo in the 3,000 fps category, so a 20" will give you about 120 fps more MV than a 16".

If your shooting will be confined to shorter ranges, probably won't make a noticeable difference in accuracy if you go 16". If you expect to reach out, the longer the barrel the better.

Mechanical accuracy - that is, of the weapon, has nothing to do with the length of the barrel.  It does affect sight radius, which affects your ability to aim the weapon precisely.  Longer is better.  

But as Joe correctly stated, you give up velocity with a shorter barrel, which is what makes the .223 a leathal military weapon instead of a .22 Rimfire.

If you are only interested in under 300yd work, the 16" is fine.  Since legal limit is 16", get a real 16" barrel, not a 14.5" or shorter with a permanently attached "muzzle device".  The "muzzle devices" don't add any velocity over the base barrrel length.

Warmly, Col. Colt

Thanks.

I'm beginning to re-consider my option on optics. With the fact that I can just as easily hit a man sized target up to 250yds with a full size AR15 rifle using irons, what is the point of a scoped carbine?

I'll prolly be leaning toward a 20" barrel.

Think of the terminal ballistics when factoring accuracy.
If your bullets fragment range is only 175 yards.......
A 14.5 should get you center mass at will out to 200 yards.
If you want a target .223, a 20-24" DCM with bipod and proper ammo should do the trick.

For some of us, a man sized target it not what we shoot at. It's generally more like a coyote or a little woodchuck sized target and they are generally scurrying around all over the place.  hts  Since it's hard to justify self defense when shooting people past just a few yards, I really wouldn't worry about your fragmentation past lets say 50 yards. Having said that, there is plenty of good ammo out there that will be plenty enough to shoot coyote sized game past 300 yds with a 16" barrel, and a 16" barrel is alot easier to swing in CQB if you ever have to get down and dirty. Makes for the best of both worlds IMHO. Just my .02

Quoted: For some of us, a man sized target it not what we shoot at. It's generally more like a coyote or a little woodchuck sized target and they are generally scurrying around all over the place.   You'll need better sights than irons for such work. I like to have a nice 12-14X scope with quick disconnect rings(like ARMS), so when I'm done plinking vermin, the eotech can get back on to give me peace of mind at night    Since it's hard to justify self defense when shooting people past just a few yards, I really wouldn't worry about your fragmentation past lets say 50 yards. Having said that, there is plenty of good ammo out there that will be plenty enough to shoot coyote sized game past 300 yds with a 16" barrel, and a 16" barrel is alot easier to swing in CQB if you ever have to get down and dirty. Makes for the best of both worlds IMHO. Just my .02

Uhh... I'll be hunting aliens in wheat fields, what do you recommend?

Quoted: Quoted: For some of us, a man sized target it not what we shoot at. It's generally more like a coyote or a little woodchuck sized target and they are generally scurrying around all over the place.   You'll need better sights than irons for such work. I like to have a nice 12-14X scope with quick disconnect rings(like ARMS), so when I'm done plinking vermin, the eotech can get back on to give me peace of mind at night    Since it's hard to justify self defense when shooting people past just a few yards, I really wouldn't worry about your fragmentation past lets say 50 yards. Having said that, there is plenty of good ammo out there that will be plenty enough to shoot coyote sized game past 300 yds with a 16" barrel, and a 16" barrel is alot easier to swing in CQB if you ever have to get down and dirty. Makes for the best of both worlds IMHO. Just my .02 Uhh... I'll be hunting aliens in wheat fields, what do you recommend?

16" combine!

Quoted: Think of the terminal ballistics when factoring accuracy. If your bullets fragment range is only 175 yards....... A 14.5 should get you center mass at will out to 200 yards. If you want a target .223, a 20-24" DCM with bipod and proper ammo should do the trick.

Trouble is, you are NOT going to get fragmentation at 175 yards, with a 14.5 inch barrel. 95 to 100 meters at best with M193 ball and 45 to 50 meters at best with M855. While a 14.5 inch barrel IS capable of center mass hits at 200 yards, fragmentation will NOT happen at that distance, or even close to it. That is maximum range for M193 ball in a 20 inch barrel to fragment, 150 meters if M855.

See the Ammo Oracle.



Lonny

There's much better bullets out there than m193 and m855 for distance shots, so to choose a rifle based on shitty ammo is pretty foolish IMO. Sure, at close range, it fragments well, but at longer distance, a good 65 grain HP will be much better.

For Aliens in wheat feilds, I suggest a good mil spec Acme alien incinerator model 182. Anything else is inhumane.