10.5, 11.5 or 12.5 Differences

[ARCHIVED THREAD] - 10.5, 11.5 or 12.5 Differences

Posted: 8/5/2017 3:49:18 PM EDT

Other than length what's the difference? Is one considered more reliable?
Seems most run a rail over gas block, but I want to do a stock A2.

Posted: 8/5/2017 4:10:55 PM EDT

[#1]

Quoted:
Other than length what's the difference? Is one considered more reliable?
Seems most run a rail over gas block, but I want to do a stock A2.

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The shorter the barrel/gas system length, the shorter the dwell time. Shorter dwell time can cause extraction problems if the rifle is running too fast. This can be controlled with an adjustable gas block, but since you want to have an A2 look, you'll have to use a heavier buffer to slow it down.

If you're looking for something a little more classic looking,

Del-Ton 11.5 kit

This kit comes with an H1 buffer, but you might have to play around with buffer weights to get it right.

Posted: 8/5/2017 6:45:22 PM EDT

[#2]

I have a 10.5" from LMT and it has been nothing but reliable for a few thousand rounds. Some of which has been several hundred round multi day courses with no cleaning and just daily lubing.

It also has been reliable with all ammo too. From Tula and Wolf to good NATO spec stuff.

Posted: 8/5/2017 7:23:07 PM EDT

[#3]

A bit of velocity. A user did a great comparison over on the ar15 ammo sub-board recently. 12.5" in many loads chrono'd much more like a 14.5" and 11.5" in a lot of loads had minimal difference from a 10.5"; that was my take away at least.

As far as the reliability; while it should technically be true that the longer barrels are more reliable than a 10" gun with good components I've had great luck with 10" guns and never seen or known of anyone with reliability issues with good 10" setups.

Posted: 8/5/2017 10:27:58 PM EDT

[#4]

Quote History

Quoted:
A bit of velocity. A user did a great comparison over on the ar15 ammo sub-board recently. 12.5" in many loads chrono'd much more like a 14.5" and 11.5" in a lot of loads had minimal difference from a 10.5"; that was my take away at least.

As far as the reliability; while it should technically be true that the longer barrels are more reliable than a 10" gun with good components I've had great luck with 10" guns and never seen or known of anyone with reliability issues with good 10" setups.

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I general rule of thumb with almost every load in an AR is going to be 50fps/inch lost in shorter barrels. I've found this to be true for my 18, 16, 12.5, and 10.5.
Only the slowest powders don't seem to follow this trend for me for some reason.
Example- H380 with 45 grain Sinterfire frangible projos. Average fps loss/inch is closer to 20.

Posted: 8/6/2017 12:42:16 AM EDT

[#5]

Do you shoot with a support arms extended? 12" barrel allows 11" rail which gives you more rail-estate. Also doesn't crowd you light, laser, BUIS etc.

Longer dwell time increases reliability, even if only slightly.

Posted: 8/7/2017 3:22:58 PM EDT

[#6]

The manufacturer is probably the biggest determinant when it comes to the reliability of your rifle. I have owned all 3 of these lengths and there is little difference. I use a 10.5" LMT right now.

Posted: 8/7/2017 4:00:11 PM EDT

[#7]

I have a Colt and a Bushmaster with 10.5" barrels. Adco did both and I assume they adjusted the gas port. Both guns were 16" and have no mods after the chop. Both run fine with or without the suppressor. I don't know why some folks have so many problems getting them running. I guess some times it is better for me to be lucky than good.

Posted: 8/17/2017 12:36:59 AM EDT

[#8]

Quote History

Quoted:
I general rule of thumb with almost every load in an AR is going to be 50fps/inch lost in shorter barrels. I've found this to be true for my 18, 16, 12.5, and 10.5.
Only the slowest powders don't seem to follow this trend for me for some reason.
Example- H380 with 45 grain Sinterfire frangible projos. Average fps loss/inch is closer to 20.

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Quote History

Quoted:

Quoted:
A bit of velocity. A user did a great comparison over on the ar15 ammo sub-board recently. 12.5" in many loads chrono'd much more like a 14.5" and 11.5" in a lot of loads had minimal difference from a 10.5"; that was my take away at least.

As far as the reliability; while it should technically be true that the longer barrels are more reliable than a 10" gun with good components I've had great luck with 10" guns and never seen or known of anyone with reliability issues with good 10" setups.

I general rule of thumb with almost every load in an AR is going to be 50fps/inch lost in shorter barrels. I've found this to be true for my 18, 16, 12.5, and 10.5.
Only the slowest powders don't seem to follow this trend for me for some reason.
Example- H380 with 45 grain Sinterfire frangible projos. Average fps loss/inch is closer to 20.

Here's the thread: http://www.ar15.com/forums/t_3_16/714088_Suppressed-5-56-SBR-Velocity-Tests--41-Factory-Loads-from-10-5--11-5--12-5-and-14-5-ALL-DONE-.html

I've heard the 50fps rule forever but that didn't hold true in my testing.

Posted: 8/23/2017 3:29:18 AM EDT

[#9]

Velocity will be sort of all over the place based on the material, finish/lining, and rifling type of your barrel, plus individual variation from barrel to barrel. I have a 12.5 that shoots faster than most 14.5's

Posted: 8/23/2017 5:16:50 AM EDT

[#10]

Major differences are velocity and length. The 10.5" is the shortest and would be the easiest to move around indoors. The 12.5" gives you the most velocity, but ya know it's a tad bit longer. I love the 11.5" barrel the best, decent velocity and still very short. I think you'll be happy any way you go though, it's not that huge of a difference, ha

Posted: 8/23/2017 10:58:59 AM EDT

[#11]

The velocity difference is insignificant (if it even exists) for the above reasons. Dwell time can be a factor, but only really matters if you get failures. There will be greater wear on your extractor parts, but it takes most shooters years to wear that stuff out anyway, so I wouldn't worry about it.

The length difference of 10.3" vs 11.5" is most noticeable when adding a sound suppressor. If you won't be using one, I recommend an 11.5" barrel.

Posted: 8/23/2017 1:00:05 PM EDT

[#12]

FWIW my Ballistic Advantage 10.5 with M16 BCG and H2 buffer has been flawless suppressed and unsuppressed using everything from Wolf to M855 NATO.

Posted: 8/23/2017 1:06:13 PM EDT

[#13]

Like any AR barrel, longer is better in every way except handling.

Posted: 8/24/2017 12:32:04 PM EDT

[#14]

I have Colt 11.5 inch, Noveske N4 10.5 inch, and LMT 10.5 inch guns. All have been 100% reliable when fired semiauto, fullauto, suppressed, unsuppressed....so long as they are appropriately lubed.

I personally prefer 10.5s for their shorter OAL.

Side note, the Gemtech suppressed bolt carrier is OUTSTANDING in a 10.5. A friend has one in his 10.5" LMT MRP upper. It makes for a very nice shooting suppressed 10.5 with zero gas blowback to the shooter. Here are some videos (a friend's channel, not mine) of my Colt M16 lower, h3 buffer wearing a friend's LMT MRP 10.5 upper, Gemtech SBC, SiCo Saker 762 with Dead Air Key-Mo mount.

https://m.youtube.com/watch?v=d5eI8TswUFg

https://m.youtube.com/watch?v=1SdWE5y-F3w

https://m.youtube.com/watch?v=1RqJ5_qiokg

Oh and a 10.5 vs 11.5 discussion wouldn't be complete without linking this:

Paul Buffione on 10.5 vs. 11.5

Posted: 8/24/2017 12:37:10 PM EDT

[#15]

I like the idea of getting an 11.5in barrel and then pin and welding one of the new Trek II silencers to it, that way you're only paying for a single stamp. I wonder how well the can would hold up without any sort of sacrificial baffle.

Posted: 8/24/2017 12:44:13 PM EDT

[#16]

Quote History

Quoted:
I like the idea of getting an 11.5in barrel and then pin and welding one of the new Trek II silencers to it, that way you're only paying for a single stamp. I wonder how well the can would hold up without any sort of sacrificial baffle.

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Cut a barrel down. Even then you'll be overgassed. An 11.5 will commonly have a .076" port but you only need something like .055" with a can.

Posted: 8/24/2017 1:01:37 PM EDT

[#17]

The latest DD MK18 barrels are .070" but they will swap out if you have an older one.
I read an article about drilling & tapping a set screw into the gas block to change orifice size, but haven't done it. Adjustable GBs aren't terribly expensive though.

Posted: 8/25/2017 10:05:34 AM EDT

[#18]

I remember reading a barrel length test on here. From 10.3 to 11.5 you gain something like 150 fps more. That's pretty huge considering the barrel is only 1.2 inches longer.

Posted: 8/25/2017 10:50:50 AM EDT

[#19]

That can happen, but it's uncommon. That's essentially the greatest difference achievable, and a difference of 150 fps is relatively insignificant.

There are just too many variables to set a number that high as the average difference. Most of the time the difference will be less.

Posted: 8/25/2017 11:13:19 AM EDT

[#20]

I went 11.5" because it's a good compromise between reliability and handling. No ragrets.

Posted: 8/27/2017 8:06:50 PM EDT

[#21]

Quote History

Quoted:
Velocity will be sort of all over the place based on the material, finish/lining, and rifling type of your barrel, plus individual variation from barrel to barrel. I have a 12.5 that shoots faster than most 14.5's

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@boltcatch.

Lol what? Please post proof of your 12.5" velocities faster than a 14.5 using the same ammo. You can't change physics.

Posted: 8/27/2017 10:00:36 PM EDT

[#22]

Quote History

Quoted:

@boltcatch.

Lol what? Please post proof of your 12.5" velocities faster than a 14.5 using the same ammo. You can't change physics.

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It's well known that certain materials - usually stainless - will shoot faster than a regular chrome lined barrel; throw in polygonal rifling, then look at a short barrel that is on the faster end vs. a longer barrel that is no the slower end, and there you go. It's not an apples-to-apples comparison other than using the same ammo in the same ambient temps and conditions.

I have a chrono and a bunch of barrels and have been handloading for years - and last time I checked, I'm capable of reading an LCD display.

Posted: 8/28/2017 7:59:52 PM EDT

[#23]

Quote History

Quoted:

It's well known that certain materials - usually stainless - will shoot faster than a regular chrome lined barrel; throw in polygonal rifling, then look at a short barrel that is on the faster end vs. a longer barrel that is no the slower end, and there you go. It's not an apples-to-apples comparison other than using the same ammo in the same ambient temps and conditions.

I have a chrono and a bunch of barrels and have been handloading for years - and last time I checked, I'm capable of reading an LCD display.

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Please post at least one anecdotal piece of evidence of a 12.5" barrel with higher velocities than a 14.5" barrel using the same ammo under similar conditions. Otherwise it seems like you were implying you can achieve 14.5" velocities out of a 12.5" barrel. Also link to the magic barrel so we can all upgrade our sbrs. Thanks.

Posted: 8/28/2017 8:04:42 PM EDT

[#24]

Quote History

Quoted:

Please post at least one anecdotal piece of evidence of a 12.5" barrel with higher velocities than a 14.5" barrel using the same ammo under similar conditions. Otherwise it seems like you were implying you can achieve 14.5" velocities out of a 12.5" barrel. Also link to the magic barrel so we can all upgrade our sbrs. Thanks.

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I know of s number of Noveske 12.5s that are faster than issue M4 barrels.