Barrel Length 10.5 - 12" Why?

[Armati]

I have seen shorty bbls in 10.5, 11.5, and 12". Why?

The engineers who built them couldn't possibly just came up with these lengths at random. What is gained from each? Thanks.

[LukeMacGillie]

The ability to get into, deploy out of and if need be engage targets from the front seat of a land crusier:p

Its a trade off that worth it in terms of being able to engage the closer target.

[KevinB]

There are factory 5.56mm bbl's in at LEAST all of the following:
4"
5.5"
6"
7.5"
8"
9"
10"
10.3"
10.5"
11.5"
12.0"
12.5"
13.7"
14"
14.5"
16"
16.5"
17"
18"
20"
22"
24"


Everyone working to find the best mix for them.

Port Pressures (can or no can), Velocities, Accuracy, Manuverability/OAL limits(many things also I dont have a clue about) etc. are all different from user group to user group.
Hence the never ending search to find the ultimate length

[baffle Stack]

4"?!
that's about as long as my G19:eek:
http://img.photobucket.com/albums/v499/cybin/alucard.jpg

[KevinB]

http://img.photobucket.com/albums/v193/EvilKev/Weapons/4inchPDW.jpg

Somewhere at home I think I have some pics of shooting it -- with and without the can. I still have a 4" upper somewhere -- in my pile of stuff I will NEVER use

[C4IGrant]

I have seen shorty bbls in 10.5, 11.5, and 12". Why?

The engineers who built them couldn't possibly just came up with these lengths at random. What is gained from each? Thanks.

7.5 and 10.5 seem to be the most popular followed by 11.5. 12" barrels are also catching on as they are going to be more reliable.

For CQB and operating out of vehicles they are an excellent choice. The problem is that many of them do not run very well. A gas piston driven AR in these barrel lengths is really the best way to go IMHO.


C4

[rob_s]

I don't know if it answers the OP's question or not, but I'm glad that I went with an 11.5" as it allowed me to mount my Ops 15th model silencer without any kind of barrel extension. It makes for an overall package that's shorter than my 16" barrel with A2 birdcage.

[Robb Jensen]

IIRC 10.3" was only ever used because they were cutting down factory 14.5" M4 barrels and this is where the 203 stepdown is.

[Derek_Connor]

I have not done any testing myself, but some information at 10-8 was posted about the 12.5 barrel and its velocity


Per 10-8, author of the thread seems to be Tom Alibrando, and the data below was provided by Wes @ MSTN:



NOVESKE S/S POLYGONAL 1X7" 12.5" ......... LMT CHROME LINED 1X7" 14.5"

M193 .......................... 2948 FPS .............................. 2984 FPS

M855 .......................... 2836 FPS .............................. 2861 FPS

MK 262 ....................... 2602 FPS .............................. 2576 FPS




NOVESKE S/S POLYGONAL 1X7" 16" ....................LMT S/S 1X7" 18"

M193 .......................... 3135 FPS .............................. 3177 FPS

M855 .......................... 3004 FPS .............................. 3026 FPS

MK 262 ....................... 2723 FPS .............................. 2744 FPS




12.5 is T.O.G., the ultimate "do it all barrel" from my last 2 classes...

Its handy with the can on or without the can on, its nimble with an aimpoint and gets hits on target very quickly, or I can put a 1-4x power optic on and get a little specific..

Also, per the same thread (http://www.10-8forums.com/ubbthreads/showflat.php?Number=30623&page=) all credit goes to a Dennis Wong for doing the graphs:

http://img138.imageshack.us/img138/5663/75zl7.jpg

http://img138.imageshack.us/img138/416/62jw8.jpg

http://img138.imageshack.us/img138/2938/55wo3.jpg


Graphs showing respective three round shots using different grain bullets

[AR15barrels]

IIRC 10.3" was only ever used because they were cutting down factory 14.5" M4 barrels and this is where the 203 stepdown is.

If you cut an M4 barrel in the M203 cut so that you get maximum usable barrel length with the new shoulder right at the point where the taper meets the 0.720" diameter area, the barrel comes out to about 11.3" long.

I just did one the other day in fact so that's why the number is still fresh in my mind.

[AR15barrels]

I have not done any testing myself, but some information at 10-8 was posted about the 12.5 barrel and its velocity


Do the tests yourself.
Don't rely on the errornet.

I have seen conflicting tests where chrome lined and Noveske barrels of the same length are giving the same velocity.

The data you posted is often used to justify (sell) Noveske barrels so it's suspect right off-the-bat.

Even having said that, 12" or 12.5" is a very good length.
It has just enough gas system dwell to start being very reliable with a wide range of ammo.

You can't go wrong with one of Noveske's barrels.

[UPSguy]

Here is a link to my 12.5" Noveske testing from a few weeks ago.

https://www.m4carbine.net/showthread.php?t=5119

[Robb Jensen]

If you cut an M4 barrel in the M203 cut so that you get maximum usable barrel length with the new shoulder right at the point where the taper meets the 0.720" diameter area, the barrel comes out to about 11.3" long.

I just did one the other day in fact so that's why the number is still fresh in my mind.


I guess I should have cleared that up. To be as close to the 10.5" LMT factory barrel Crane cut them to 10.3". Which is at the rear edge of the 203 notch. They could have run 10.5" factory barrels and some 11.5"s but being this is for the Military they probably wanted them to appear the same and have similar velocities.

[AR15barrels]

I guess I should have cleared that up. To be as close to the 10.5" LMT factory barrel Crane cut them to 10.3". Which is at the rear edge of the 203 notch. They could have run 10.5" factory barrels and some 11.5"s but being this is for the Military they probably wanted them to appear the same and have similar velocities.

Reference material:

http://ar15barrels.com/tech/m4a1.jpg

http://ar15barrels.com/tech/ar15bolt-extension.gif

Add up 10.062" and 0.75" and you are at 10.8" if you were to cut an M4 barrel at the rear edge of the M203 cut.

[Robb Jensen]

Reference material:
http://ar15barrels.com/tech/m4a1.jpg
http://ar15barrels.com/tech/ar15bolt-extension.gif

Add up 10.062" and 0.75" and you are at 10.8" if you were to cut an M4 barrel at the rear edge of the M203 cut.

Maybe they didn't measure twice and cut once! ;)

I can think of no other reason for 10.3" and then later buying LMT 10.5" barrels that makes any since.

Perhaps they wanted them as short as possible using the suppressors they were/are using and 10.3" was it. Maybe they figured out it was just cheaper buying 10.5" barrels.