I was curious if anyone knew at about what range a 16" Colt LE6920 or any 16" 1:7 Twist AR struggles for accuracy. In other words what is the longest range the rifle would be good for? New to this stuff just trying to decide where to go with the mods. Thanks for the input!

what kind of accuracy are you asking about?  If we're talking minute-of-man, a 16" can be affective out to at least 500-600 meters.

A 16 inch isn't going to cost you anything but a little speed.

Click me

What do you mean "minute-of-man"

I'm assuming he means man sized targets?

Man-sized target.  And I'm talking about a decent shooter with non-magnified iron sights or RDS and a chrome-lined barrel.  Add a magnified scope, good shooter, SS barrel, and quality ammo to the equation and the range increases, as seen in the link provided above.

Keep in mind there is a difference between accuracy and effectiveness.  

What are you trying to do?

I have a 16" 1:9 CL YHM Black Diamond carbine that I have shot out to 300 yards so far. The optic is an Aimpoint C3 2x 1moa which is dialed in at 50 yards along with the factory irons. I can hit a 8" steel dinger with every shot without problems.

My Colt 6920 with a 3x9 scope and match ammo refuses to do  better than 1.5" at 100 yards. Is that acceptable for a fighting weapon which it is? Hell yes.
However, this has more to do with the light profile (M-4) and chrome lining than anything else. There would be no difference in accuracy between
two bull barreled varmint rifles if the only differences were barrel lengths of 16 inches vs. 20 inches. As others said, the bullet just flys a little slower out of a 16".

The chronograph readings of 55gr. handloads with M193 projectiles:

Colt 6920:                 2830 ~ish fps
Colt M-16A1 clone:  3150         fps

Well I'm trying to build it mainly for target shoooting and yote hunting. So longer distances nothing really CQ or to just run a ton of rds though. I'm looking at doing a Burris 4-12x Scope w/ YHM Flip up Iron Sights, Harris HBLMS Bipod 9-13" and I already put a Daniel Defense Lite 7.0 Rail on it. I just want to make sure I by what is going to work well the first time.

try more like 700-800 yards/   the 16 will get out out to 700-800 easy with  the right ammo, ( 77grain/MK 262)

well i would say the average standard mil-spec barrel shoots what, 2moa.  for head shots your practical to 250 yds. maybe 300.  for com shots, id say 600-700 yds.  now if you can get closer to 1 moa accuracy, your hs distance goes to 500 yds if you are perfect and com shots are extended to 800yds.  yes this is past the transonic zone but should still get you in the chest cavity... at that distance, if you need to take a shot and have the skills to hit, go for it, if will be effective if you are.

The gun in stock form will most likly out shoot you.

Don't mod it, buy ammo and go shooting

btw, length has very little to do with accuracy, and all things being the same, a shorter barrel will produce tighter groups to to increased ridigness.

Ok I'm starting to understand it now. Thanks guys for all the input!

Thanks for the article!

The accuracy will be slightly degraded as compared to a 20"bbl.  According to USMC, max effective range for a point target using an M-16 (20" bbl) is 550 meters.  IIRC, max effective is 400 on a point target with the M4.  "How accurate" is subjective (are you talking about keeping the round on a man size target or keeping it in the X ring???), but bottom line, reducing bbl length reduces accuracy at long range.  Short range isn't as big an issue.  Many (only here at AR15.com) will say the added bbl length only adds to velocity, and leave it at that.  That fails to take the next step in thinking about how that added velocity might aid in accuracy.  Simply put, the faster the round goes, the flatter the trajectory.  That means it's more forgiving if your range estimation is slightly off.  Also, the faster it goes, the less wind effect, which is also beneficial to accuracy.  So in an absolutely controlled environemnt, the barrel length might not make a huge difference in terms of long range accuracy.  But how many of us shoot in an absolutely controlled environment???  There's something to be said for the fact that sniper rifles and long range competition rifles all have outrageously long barrels....

Good word here!

I know a bit about the subject, but I am even better advised now. Yep, I get wrapped on moa at the range to the point of forgetting that my 3/4-1.5" groups will kill alot of game at quite a distance. Bushy 1:9 16" barrel.

That linked thread did show some truly spectacular accuracy with a 16", but it doesn't negate the fact that the added velocity of a longer barrel aids in accuracy.  As someone noted in that thread, had he been running a longer barrel (assuming equal quality) some of the misses would have been hits.

oh come on, everyone knows that an 11in barrel is all you need!

Velocity has nothing to do with inherent accuracy, but it will have a straighter trajectory.

Most accurate Upper I own now is my Larue Stealth... it's 16" and
magically got a .981" (only 5 shots, but still) group at 200m today...
with 69gr Prvi match ammo...  I haven't even worked up a handload for
this upper yet...





Will I ever need that kind of accuracy? 100% serious when I say
"Nope!"  My BCM upper gives me all the accuracy I need (1.5-2 moa w/
Wolf)... but extreme accuracy is still fun to play with...

Are you seriously trying to equate the long range accuracy of the 5.56mm, chrome lined, NATO chambered barrel on the 6920 to that of a sub-MOA .308 barrel?

Awwweee   $h!t.... someone just poked the bear...





Molon w/ the Empirical-bitch-slap incoming.

Wow, great point.  I totally missed that when I skimmed the linked thread -  without realizing it I assumed nobody would do such an apples to oranges comparison.  Bad assumption.

Still waiting to hear why snipers and long range competitors choose ultra long barrels if the shorter ones are equally or more accurate....

velocity is why.



Less time in flight for the projectile... less wind effect... farther fragmentation range...

Say what?
And this
Dont forget this too.

EXACTLY!  Less wind effect = better real world accuracy.  Flatter trajectory = better real world accuracy.  Better terminal performance is certainly one of the longer barrel benefits for snipers.  But for long range competition (shooting at paper) terminal performance doesn't matter.  So for snipers the benefits are better accuracy and better terminal performance.  For competitors it simply comes down to better accuracy.

Believe it or not, I agree with those articles.  They make perfect sense.  But one thing that has to be considered for all of them - they were not about PUSHING THE ENVELOPE range-wise.  They make excellent points about barrel length not being of real concern to accuracy...at distances that are not taxing for the round.  

In fact, the first article actually acknowledges that the added velocity IS important when it comes to pushing the envelope in distance.  It stated that "The common reason for opting for the .300 Win. Mag. that it extends the capabilities of the rifle to longer ranges than the .308 Winchester is capable in those rare situations where longer range capability is necessary."  Given that the thing the .300 win mag has over the .308 is a hell of a lot more velocity, this statement (which they are not arguing against) in and of itself means added velocity helps accuracy.  But that's not the only place where they make this point.  They then chopped the 300 win mag's 26" barrel down incrementally and found no velocity loss until going past 22".  This means the particular load they employed did not need those extra 4".  The article states that "as a result of their tests, Tac Ops decided not to go below 22 inches on their .300 Win. Mag. tactical precision rifle."  So now ask yourself this question:  If the goal was to maintain utmost long range capability, while not using more barrel than necessary, why did they decide that it was acceptable to cut off barrel length ONLY UNTIL VELOCITY WAS EFFECTED?  The answer is crystal clear: velocity is a factor in long range accuracy.

Now that particuliar load didn't need more than 22" to attain full powder burn, so anything over 22" was overkill.  But what about other loads?  There are loads that will need more length to attain full velocity potential.  And there are other loads that would require LESS than 22."  But the fact is, they decided that reducing velocity would reduce their long range potential.

These articles prove that there are barrels that are longer than necessary to realize their full potential using a particuliar load.  They also prove that at certain ranges, in certain applications, length reduction is beneficial because the benefits of less barrel whip outweigh the benefits of added velocity.  They also prove that in urban environments (read relatively short range), a sniper rifle does not need the benefits of a little added velocity.  They also prove that when you're pushing the accuracy envelope in distance added velocity helps.  Tying this back in to ARs, it's well documented that with most if not all loads, a 16" barrel looses velocity compared to a 20".  Therefore (all else being equal) the 20" will have superior accuracy at ultra long range.  If the added velocity didn't matter we'd all be shooting snubnose rifles.    

Reread those articles being careful not to make inferrences that don't work.  Also be aware of exactly what points they are proving, and what points they are not proving.  They're great articles, grounded in perfect logic.  But the points they make do not state that when pushing the envelope range-wise velocity doesn't matter.  And in fact the first article makes the opposite point.

Why don't you just write a damn book?

Its not about barrel length - its about the short sight radius on a true carbine. That's what defines he accuracy, which is not great with the irons. If you go with a mid-length carbine with 3" more between the sights which will in turn be more accurate. If you use a scope, all those questions go out the window. Then, all things being equal, your 16" will print slightly differently than a 20" because of different velocities, but the group sizes should be similar.