Anyone directly compared 14.5" vs 16" velocity?

[jzerfoss]

Not really looking for opinions on whats better and why or estimations. Just looking for a direct velocity comparisons between 14.5" vs 16" with mid length gas system.

 

[TonyTheTiger]

Yes.

 

[jzerfoss]

I assume by direct comparison, you mean chopping the same barrel back from 16" to 14.5". I can only offer a two different barrel comparison of the same ammo. I'll shoot them both tomorrow and report back. From what little I can remember from shooting them side by side it was negligible.

16" ARP 3 groove stainless button rifled (Dominus)
vs.
14.5" Griffin HEDP nitrided button rifled (MG7)
vs.
13.7" ARP 3 groove CM melonited button rifled (MG7)

Nice, I've read several articles on it with bolt actions and ARs but the results vary greatly. Anywhere from 25 to 150+fps difference in 14/14.5" to 16" using the same ammo. I was curious to know if anyone here had tried it.

 

[MSTN]

Great question!

Circa 2003, from my youngest son's 7th grade science fair project:

14.5" LMT C/L BARREL W/ NATO CHAMBER

M193 2984 FPS
M855 2861 FPS
MK262 2669 FPS

16" LMT C/L BARREL W/ NATO CHAMBER

M193 3075 FPS
M855 2938 FPS
MK262 2769 FPS

This was a in truth a scientifically meaningless test of just two barrels with one lot each of ammo with what today would be considered at best a questionable chronograph.

[We won the science fair for the entire school, BTW. Could not get away with that in today's "woke" climate.]

Pat Rogers (RIP) used this data (plus much more info from the project) in multiple published articles.

Yes, chronographs truly sucked back then compared to what we have today. But at least this was real Mil-Spec ammo. There was no "X" in front of any of the ammo's designation. It was all the real thing.




You didn't ask, but my opinion is every AR' 5.56 barrel length has a corresponding optimum gas system length.

10.5" carbine length

11.5" carbine +1*

12.5" carbine +1 or mid-length (suppressed only)

14.5" mid-length*

16" intermediate length*

18" rifle length

Adjustable gas blocks on everything.

I see no "practical tactical" use in longer barrels in 5.56. I own nothing longer than 16" in this caliber.

* my favorites

 

[jzerfoss]

Great question!

Circa 2003, from my youngest son's 7th grade science fair project:

14.5" LMT C/L BARREL W/ NATO CHAMBER

M193 2984 FPS
M855 2861 FPS
MK262 2669 FPS

16" LMT C/L BARREL W/ NATO CHAMBER

M193 3075 FPS
M855 2938 FPS
MK262 2769 FPS

This was a in truth a scientifically meaningless test of just two barrels with one lot each of ammo with what today would be considered at best a questionable chronograph.

[We won the science fair for the entire school, BTW. Could not get away with that in today's "woke" climate.]

Pat Rogers (RIP) used this data (plus much more info from the project) in multiple published articles.

Yes, chronographs truly sucked back then compared to what we have today. But at least this was real Mil-Spec ammo. There was no "X" in front of any of the ammo's designation. It was all the real thing.




You didn't ask, but my opinion is every AR' 5.56 barrel length has a corresponding optimum gas system length.

10.5" carbine length

11.5" carbine +1*

12.5" carbine +1 or mid-length (suppressed only)

14.5" mid-length*

16" intermediate length*

18" rifle length

Adjustable gas blocks on everything.

I see no "practical tactical" use in longer barrels in 5.56. I own nothing longer than 16" in this caliber.

* my favorites

Good info man. Your data seems to reflect the average of what I've seen with other tests online with around a 75-100fps gain going from 14.5 to 16". Also, with other tests I've seen almost no gain going from 16" to 18" which is surprising. Thanks for the info.

 

[TonyTheTiger]

Just went and reviewed my data. The barrels lengths I've chrono'd recently enough to have used a common load between them are: 13.7, 14, multiple 14.5, 14.8, 15, multiple 16, 17, 18, and 22. I've had fast 14.5's that are faster than slow 16's, but aggregating the data says that 40-55fps per inch below 16" is to be expected with heavy bullet loads, and slightly less loss with mil spec equivalent 55gr stuff. Above 16" it averages around the 20-30fps per inch that is the common rule of thumb. Some day I'll get more data for 12.5". I hate my 10.5" so no data or interest in gathering it.

 

[Molon]

Just looking for a direct velocity comparisons between 14.5" vs 16" with mid length gas system.

Any difference in muzzle velocity due to a difference in the length of a mid-length gas system versus a carbine gas system is going to be miniscule and lost in the noise of other variables.

Observations On The Velocities Obtained From A Direct Impingement Gas System AR-15
Compared To A “Single Shot” AR-15​

I conducted a simple test that consisted of a comparison of the velocities obtained from an AR-15 using the direct impingement gas system with a standard sized gas block, to that of the same barrel with no gas system at all; that is, I completely clamped-off the gas port, turning the AR-15 into a "single-shot" rifle.

The ammunition used in this test was hand-loaded 69 grain Sierra MatchKings. I fired three 10-shot strings of this ammunition in a row over an Oehler 35-P chronograph, with proof-screen technology. The center screen of the chronograph was positioned 21 feet from the muzzle. The test vehicle was a 16” barreled AR-15 with a carbine-length direct impingement gas system and a standard sized (0.75”) Larue Tactical low-profile gas block.

After firing the three 10-shot strings from the upper using the direct impingement system, I let the barrel cool and then removed the gas tube. Next, I removed the low profile gas block from the barrel, flipped it 180 degrees and reinstalled it on the barrel, thereby completely clamping off the gas port on the barrel. This gave me a single-shot AR-15 in which I had to manually load and eject each round using the charging handle, thus giving me the means to determine the amount of velocity that is lost due to the auto-loading function of the direct impingement gas system of the AR-15.

Following the same procedure as previously used, I fired three 10-shot strings of the same hand-loaded 69 grain Sierra MatchKings over the Oehler 35-P chronograph positioned 21 feet from the muzzle using the single-shot AR-15. The results are show in the table below.

As you can see in the table below, there was a small (but statistically significant) difference of 23 FPS between the grand averages of the velocities from the direct impingement gas system and the single-shot (gas port clamped-off) system.

Atmospheric Conditions


Temperature- 63 degrees F
Humidity - 34%
Barometric pressure – 30.20
Elevation - 960 feet above sea level
Skies – sunny, Jupiter aligned with Mars



+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
===========================================================

 

[jzerfoss]

Any difference in muzzle velocity due to a difference in the length of a mid-length gas system versus a carbine gas system is going to be miniscule and lost in the noise of other variables.

Observations On The Velocities Obtained From A Direct Impingement Gas System AR-15
Compared To A “Single Shot” AR-15​

I conducted a simple test that consisted of a comparison of the velocities obtained from an AR-15 using the direct impingement gas system with a standard sized gas block, to that of the same barrel with no gas system at all; that is, I completely clamped-off the gas port, turning the AR-15 into a "single-shot" rifle.

The ammunition used in this test was hand-loaded 69 grain Sierra MatchKings. I fired three 10-shot strings of this ammunition in a row over an Oehler 35-P chronograph, with proof-screen technology. The center screen of the chronograph was positioned 21 feet from the muzzle. The test vehicle was a 16” barreled AR-15 with a carbine-length direct impingement gas system and a standard sized (0.75”) Larue Tactical low-profile gas block.

After firing the three 10-shot strings from the upper using the direct impingement system, I let the barrel cool and then removed the gas tube. Next, I removed the low profile gas block from the barrel, flipped it 180 degrees and reinstalled it on the barrel, thereby completely clamping off the gas port on the barrel. This gave me a single-shot AR-15 in which I had to manually load and eject each round using the charging handle, thus giving me the means to determine the amount of velocity that is lost due to the auto-loading function of the direct impingement gas system of the AR-15.

Following the same procedure as previously used, I fired three 10-shot strings of the same hand-loaded 69 grain Sierra MatchKings over the Oehler 35-P chronograph positioned 21 feet from the muzzle using the single-shot AR-15. The results are show in the table below.

As you can see in the table below, there was a small (but statistically significant) difference of 23 FPS between the grand averages of the velocities from the direct impingement gas system and the single-shot (gas port clamped-off) system.

Atmospheric Conditions


Temperature- 63 degrees F
Humidity - 34%
Barometric pressure – 30.20
Elevation - 960 feet above sea level
Skies – sunny, Jupiter aligned with Mars



+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
===========================================================

Great data. Interesting to see the differences in each situation. Thank you

 

[TonyTheTiger]

@reubenski almost 2800fps with 69's from a 13.7" is hauling. How much extra fps do you think the suppressor is adding? And do you see good accuracy with H335?

 

[jzerfoss]

@jzerfoss You did not ask this and I assume you have already thought of it. But I think for most people a factor in trying to decide the length is mounting a suppressor. A 13.7 or 14.5 in can be pinned in welded to get to 16. So if you're using a suppressor that already has an adapter and requires a muzzle device, it kind of makes sense. But if you can simply direct thread your suppressor to a 16 inch barrel without needing a muzzle device. It is usually the same length and weighs less overall. And more velocity. A TBAC Dominus CB is really good for a 16-in AR application.

I'm mostly debating whether or not the velocity loss is worth the 1.5" OAL less on what would be a multiple role rifle. I'm thinking I'm going to stick with 16" for the simplicity(no pin/weld)and for what seems to be on average decent velocity bump. Thank you for taking the time to post your results.

 

[carbonbased]

Here's what I saw recently on this subject. It's from 2015. Fellow cut the same barrel down and ran tests.

Go easy on me, just had cataract surgery today, feeling woozy. Can't read well, so maybe this has been discounted on this thread already. Also, the twist was 1:12″, which the author notes is not ideal. I wouldn've thought if one was going to go through all this trouble he'd get a 1:7", but whatever.

223 Remington/ 5.56mm NATO barrel length and velocity: 26 inches to 6 inches

Have you ever wondered how much barrel length effects muzzle velocity on your rifle? Well I did, so I cut up rifles chambered in 223 Remington, 308 Winchester, 7 mm Remington Magnum and 300 Winche…

rifleshooter.com

Notice the biggest change was from 16.5" to 14" but of course that's 2.5" and the other jumps are 1". Too bad he didn't do 16" & 15". Oh well.

edit: he also didn't crown the barrel each time and it seems the barrel was pretty shot out (Black Hills load shot 6 MOA!)

 

[jzerfoss]

I found a neat GA dual-lok muzzle brake that only adds .5"~ length and has a taper and locks. It's like a mini OTB brake. So you can run a 16" instead of a 13.9 or 14.5 pin/weld so you get the velocity bump and it's only around .5" longer overall.

 

[r.tenorio671]

....here's an old chart that AAC did when developing the 300BLK....