View Full Version : 12.5 inch barrel vs 13.7 inch barrel velocity
SHARPSHOOTER282
03-27-24, 08:18
can anyone tell me what the velocity difference is generally between a 12.5 inch barrel and the 13.7 inch barrel , 5.56mm ?? is velocity difference worth the longer barrel ? I notice the new UK ranger rifle (knight armament) is a 13.7 inch barrel.
can anyone tell me what the velocity difference is generally between a 12.5 inch barrel and the 13.7 inch barrel , 5.56mm ?? is velocity difference worth the longer barrel ? I notice the new UK ranger rifle (knight armament) is a 13.7 inch barrel.
There's formulas for such things around here or online, as well as various YT vids of people testing such things. The bullet itself is an issue as to terminal ballistics, and what UK will be using. I think they use the L31A1 but not sure if that's still correct. Others here will know that info.
Plan on 40-80 fps, depending on ammo weight and pressure. Be aware that that’s within the normal variation for barrels that are the same lengths. The only two good reasons to choose 13.x is A)you want to use a 12.5” barrel, but have a 12” rail, which is also about 12.5”, or B)your only silencer is a Sandman S and you can’t/won’t SBR your gun.
As to the actual KAC gun, 13.7” is social-media popular lately, and that also happens to be the shortest barrel usable with their already existing 13” handguards. Its cutting it closely enough that it could interfere with silencer compatibility.
Rifleshooter.com has published a high-quality inch by inch test that you can reference. You’ll notice that lighter projectiles lose more velocity per inch than heavier ones. If you google “Labradar 1168”, you might find a thread here with some measured velocities in 12.5” and 14.5” guns.
Anything between 12.5” and 14.5” is pretty much the sweet spot for a general purpose carbine, with 16” being an outlying exception to that rule.
Trey Knight did an interview at SHOT where he said the reason was that they had a maximum length requirement with the silencer attached. He said that was the longest barrel that they could use with their can and be under the limit enforced by the MOD requirement.
I can't vouch for any of that, but it's what he said.
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SHARPSHOOTER282
03-28-24, 06:56
would the extra barrel length from the 13.7 inch , be better for those longer range shots then the 12.5 inch ?
joedirt199
03-28-24, 07:46
More velocity is always better but 50 fps really isn't going to make a huge difference. I am cutting mine down more for size convienence over terminal velocity. Bullets hurt whether they are going 2600 fps or 2700 fps. Shortened them up to make room for suppression.
would the extra barrel length from the 13.7 inch , be better for those longer range shots then the 12.5 inch ?
It’s extremely minor, and like I said falls within variation of a given barrel length. There are 12.5” barrels that demonstrate velocities near or equal to 14.5” ones, and vice versa. Shooting appropriately zeroed 12.5” and 14.5” guns to the militarily practical limits for point target engagement, I don’t really notice the difference. It starts to become noticeable at 11.5”, for me. I’d divide practical barrel lengths into 3 groups, and within a group would see them as ballistically equal enough: 10.3”-12.5”, 12.5”-16”, and 16”-20”.
You’re simply not going to see a practical difference in bullet flight or impact between a 13.7” and a 12.5” or 14.5”. With a 50yd zero, its a 1/2moa difference at 500 yards, on a 2-3moa gun. The 50fps advantage is reduced to 35fps at that distance. Negligible.
I’d still personally choose a 14.5”-15” gun for a P/W, though 13.5” guns make great SBRs.
Eh, go with 13” and act like you have discovered the true best thing.
https://i.imgur.com/40gPNiA.jpeg
Eh, go with 13” and act like you have discovered the true best thing.
https://i.imgur.com/40gPNiA.jpegI’m putting a 13.5” in the handguard you loaned me.
Decent discussion. SF group using 10.3" out to 600 yards. Starts at 2:45:
https://www.youtube.com/watch?v=WJNPY1dCges
Decent discussion. SF group using 10.3" out to 600 yards.
We've run the 10.5 out to 750 yards... with a spotter. The only reason it's not a regular thing is because you don't put glass worthy of that distance on a 10.5 barrel. So it's irons or an RDS with crazy holdover.
I’m putting a 13.5” in the handguard you loaned me.
Nice. Cut or MosTek? Unless someone is making a 13.5” now…
Ammo selection is going to make a lot more difference than 1-2" of barrel IMO.
We've run the 10.5 out to 750 yards... with a spotter. The only reason it's not a regular thing is because you don't put glass worthy of that distance on a 10.5 barrel. So it's irons or an RDS with crazy holdover. The real problem with SBRs isn’t distance (within reason); it’s estimating that distance accurately. The shorter you go, the less forgiving of range estimation errors. Or bad data entry in your ballistic calculator.
Nice. Cut or MosTek? Unless someone is making a 13.5” now… MosTek.
The real problem with SBRs isn’t distance (within reason); it’s estimating that distance accurately. The shorter you go, the less forgiving of range estimation errors. Or bad data entry in your ballistic calculator.
Absolutely. When we shoot crazy shots like that it's just a "sling it" and correct effort. Without the spotter fixing the misses, I could should gobs of ammo and never have an idea if I was close at all.
I'm not sure I completely get the 13.7 length. I had one for a while. And, assuming you aren't going to SBR it, by the time you P&W it's the same overall length as the 14.5 P&W. Which is what I eventually sold it for. I do want to build a 12.5 SBR next and play with it along side my 10.3 and 11.5. I think the 12.5 is at the length where a compact LPVO might make sense.
SHARPSHOOTER282
03-29-24, 15:24
I'm not sure I completely get the 13.7 length. I had one for a while. And, assuming you aren't going to SBR it, by the time you P&W it's the same overall length as the 14.5 P&W. Which is what I eventually sold it for. I do want to build a 12.5 SBR next and play with it along side my 10.3 and 11.5. I think the 12.5 is at the length where a compact LPVO might make sense.
i'm siding more to the 12.5inch barrel to be honest! i have the LMT for long range . Just intrigued when i saw that uk ranger rifle uses a 13.7inch barrel - but military contracts dont always make sense
As has been mentioned, the UK KAC KS-1 contract had an overall length requirement including the suppressor. According to media, that barrel and suppressor combo meets the requirements.
As has also been mentioned, I believe, the 13.7/13.9” barrel moves a suppressor slightly to the rear. If pinned, the overall length doesn’t change unsuppressed but does suppressed. Additionally, I believe when I checked the weights on the KM6315 and KM6315-L, they were the same. So reduced barrel (and overall) weight by .4oz on a pencil barrel, reduced overall length suppressed by .8-.6” vs a 14.5 or 2.3-2.1” vs a 16, and mass shifted toward the pivot point (your body).
I probably wouldn’t get another 13.9”, personally, but neither would I get another 14.5”.
I’ve built a 12.5 mid length gas system and a 13.95 mid length. I can get you some fps with Winchester white box, pmc, or federal 223 and 5.56. It might be a while, but happy to run some numbers next time at the range with chrono.
Big fan of 12.5. If I could just have one, it would be a 12.5 carbine gas with a dot and magnifier.
Why car over Mid for the 12.5?
I go by 2% difference in MV for every inch of barrel length.
-TL
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Why car over Mid for the 12.5?
12.5 carbine is about as reliable a system you can get.
12.5 carbine is about as reliable a system you can get.
Is that for unsuppressed? I would think 12.5 mid is perfectly fine if running a can.
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Big fan of 12.5. If I could just have one, it would be a 12.5 carbine gas with a dot and magnifier.This. Or a 1-4x/1-6x.
As for carbine vs mid, it just works. Has for a long time. I somehow have yet to test this with a MG lower and shot timer, but when switching from suppressed to unsuppressed and back, “short” gas systems seem to have less drama than longer ones. Since this is the opposite of what pretty much the entire internet feels, I’m open to being wrong. But the Crane study does seem to back this up by showing a greater RoF delta, IIRC. Either way, it’s the size of the hole, not the length of the gas tube that really matters, in my opinion as someone who isn’t an engineer.
“Same gas tube as legacy guns in current use by major militaries around the world” doesn’t market as well to tinkerers (like myself) as “we made this longer for optimized suppressed use”. Since few people own suppressors, and few people will experiment while keeping variables to a miniumum, the internet is largely how people get informed about this topic, for better or for worse.
On the flipside, I doubt anything is “wrong” with a well-tuned midlength 12.5” gun, especially if left in one configuration- suppressed or not. Though unsuppressed, it will need a blowhole to be reliable when cold and dirty.
My 12.5 mid-length runs like a top. Adding a griffin dual-lok 5 soon.
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My 12.5 mid-length runs like a top. Adding a griffin dual-lok 5 soon.
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Not saying you will have an issue, but I would interested to see you do a two-day class @ 1k rounds and see how she is doing on day two.
I teach medical applications (officer down/rescue) class and it’s 2 or 3 days depending on the customer. Round count is usually 500-600 rounds per day, rifle and or pistol. Never had an issue. She gets pretty dirty, but is loved and clean regularly. I run a bcm mk2 buffer and h2 equivalent. When I get my suppressor I’ll tune her appropriately.
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I teach medical applications (officer down/rescue) class and it’s 2 or 3 days depending on the customer. Round count is usually 500-600 rounds per day, rifle and or pistol. Never had an issue. She gets pretty dirty, but is loved and clean regularly. I run a bcm mk2 buffer and h2 equivalent. When I get my suppressor I’ll tune her appropriately.
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Can you share what barrel manufacturer?
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Can you share what barrel manufacturer?
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https://faxonfirearms.com/faxon-duty-series-12-5-gunner-5-56-nato-mid-length-4150-qpq-nitride-ar-15-barrel/
I bought this back in 2014 but never installed until a few years ago. I’ve had no issues. It’s probably not the best barrel but I didn’t know what I know now. I had all the parts laying around so I threw it together.
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SHARPSHOOTER282
03-31-24, 23:51
I’ve built a 12.5 mid length gas system and a 13.95 mid length. I can get you some fps with Winchester white box, pmc, or federal 223 and 5.56. It might be a while, but happy to run some numbers next time at the range with chrono.
Cheers , that would be cool
Cheers , that would be cool
Would be extra cool if they are both from the same series from the same manufacturer.
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Strikefirst
04-03-24, 19:01
I have a 12.5 and 13.9 criterion core...I can get you velocities as soon as this lousy Michigan weather breaks.
SHARPSHOOTER282
04-04-24, 06:34
I have a 12.5 and 13.9 criterion core...I can get you velocities as soon as this lousy Michigan weather breaks.
sweet :cool:
Strikefirst
04-06-24, 12:22
American Eagle M193 average velocities
12.5 criterion core average 5 shots 2854
13.9 criterion core average 4 shots 3062
Chrono 15 feet downrange
American Eagle M193 average velocities
12.5 criterion core average 5 shots 2854
13.9 criterion core average 4 shots 3062
Chrono 15 feet downrange
Don’t bank on reproducing that with 2 other barrels, but thanks for sharing your results.
titsonritz
04-06-24, 13:24
That is pretty impressive difference for 1.4” spread.
Strikefirst
04-06-24, 14:07
The 13.9 only had 200 rounds down it when tested. Was a new builds. The 12.5 had about 500. 13.9 was shot suppressed yhm turbo t3. 12.5 shot cold u suppressed
13.9 handloaded 62gr gold dots 2.260 oal. Light crimp arplus 24.0 gr. 2766 fps avg
So, this is completely unscientific, but today my buddy chronod his 13" X95 SBR and averaged 2919 with American Eagle 55gr 60 degrees at around 400 feet elevation.
Same weather my 13.7" ballistic advantage did 2865 with M855.
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Strikefirst
04-06-24, 18:33
So, this is completely unscientific, but today my buddy chronod his 13" X95 SBR and averaged 2919 with American Eagle 55gr 60 degrees at around 400 feet elevation.
Same weather my 13.7" ballistic advantage did 2865 with M855.
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My elevation was about 820.
That is pretty impressive difference for 1.4” spread.
I'm speculating here but I bet the difference would be lower if we moved up from 55gr to 77gr at 5.56 pressure.
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The 13.9 only had 200 rounds down it when tested. Was a new builds. The 12.5 had about 500. 13.9 was shot suppressed yhm turbo t3. 12.5 shot cold u suppressed
13.9 handloaded 62gr gold dots 2.260 oal. Light crimp arplus 24.0 gr. 2766 fps avg
There's a good chance that the suppressor added a noticeable amount of velocity to the 13.9 compared to if you had shot it unsuppressed like you did the 12.5.
This link has quite a bit of suppressed chrono data for 10.5", 11.5", 12.5" & 14.5".
https://www.ar15.com/forums/ar-15/Suppressed-5-56-SBR-Velocity-Tests-41-Factory-Loads-from-10-5-11-5-12-5-and-14-5-ALL-DONE-/16-714088/
There's a good chance that the suppressor added a noticeable amount of velocity to the 13.9 compared to if you had shot it unsuppressed like you did the 12.5.
Could be.. depending on the can. I think we did a can on/off test a month ago... showed like 10 fps gain on a 10.5 if I remember correctly.
Strikefirst
04-09-24, 11:42
Next time I get out I'll test both with and without the can
joedirt199
04-09-24, 14:15
I have 11.5, 12.5, 13.5 and 14.5 I need to sight in and chrono. I will get some numbers when the weather gets better. All are BCM except the 11.5 which is an Expo heavy from Primary Arms. All are suppressed.
titsonritz
04-09-24, 14:24
I have 11.5, 12.5, 13.5 and 14.5 I need to sight in and chrono. I will get some numbers when the weather gets better. All are BCM except the 11.5 which is an Expo heavy from Primary Arms. All are suppressed.
Didn’t know BCM made a 13.5”.
joedirt199
04-09-24, 14:37
It is a cut down 16". All mid gas except for 11.5 Expo.
titsonritz
04-09-24, 19:49
It is a cut down 16". All mid gas except for 11.5 Expo.
Gotcha
There's a good chance that the suppressor added a noticeable amount of velocity to the 13.9 compared to if you had shot it unsuppressed like you did the 12.5.
Based on what? I’ve only ever heard a minimal increase and my personal testing has shown that as well.
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Based on what? I’ve only ever heard a minimal increase and my personal testing has shown that as well.
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It varies by a number of factors. It can be totally negligible, or it can make up for an inch or so of barrel, which may or may not be significant.
Based on what? I’ve only ever heard a minimal increase and my personal testing has shown that as well.
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Like the person above said, a number of factors can result in a suppressor adding a noticeable amount of velocity to a rifle (if any). In this case, I was basing it on the fact that Strikefirst was reporting a 208 fps increase in average velocity going from 12.5" to 13.9". That's a bigger difference in velocities between those two barrel lengths than I have ever seen, so I was wondering if the suppressor he was using on the 13.9 was possibly contributing to some of that increase in velocity.
Triarc published some velocity data on their barrels a while back that showed around a 100 fps increase in average velocity going from 12.5 to 13.9, so 200+ fps would be a really nice increase in velocity if its due to the barrel length alone.
joedirt199
04-14-24, 16:23
Ofcourse go to the range to chronograph and zero 7 ARs and the stupid magnetospeed 3 wouldn't read the bayonet. Atleast I got them zeroed but I still need to chrono. Got a sporter magneto that still works so just have to use that till I get the V3 sorted out. Not sure it is the cord as I tried a spare cord and still would not read the bayonet. May have to send it in to see if they can sort it out.
joedirt199
04-20-24, 14:50
Finally got to the range
11.5" Expo Heavy barrel with Banish 223 suppressor
55 TAP reload 2700
55 FMJ reload 2570
75 Hornady reload 2270
12.5 BCM cutdown Gov mid w/YHM T3
55 Tap 2833
55 FMJ 2678
75 Horn 2457
13.4" BCM cutdown mid ELW w/YHM T3
55 TAP 2810
55FMJ 2767
75 Horn 2477
14.5 BCM ELW mid w/YHM old TurboK
55 Tap 2904
55 FMJ 2773
75 Horn 2500
16 Green mountain mid unsurpressed new barrel
55 Tap 2929
55 fmj 2824
75 Horn 2511
18 WOA 3 gun interm gas w/YHM Turbok
55 Tap 3100
55 fmj 2960
75 Horn 2643
My TAP load is a 55 vmax with 24.7 Benchmark
My 55 Hornady FMJ is 25 XBR for matches
75 Hornady is over 24 varget or 26 CFE 223.
Finally got to the range
11.5" Expo Heavy barrel with Banish 223 suppressor
55 TAP reload 2700
55 FMJ reload 2570
75 Hornady reload 2270
12.5 BCM cutdown Gov mid w/YHM T3
55 Tap 2833
55 FMJ 2678
75 Horn 2457
13.4" BCM cutdown mid ELW w/YHM T3
55 TAP 2810
55FMJ 2767
75 Horn 2477
14.5 BCM ELW mid w/YHM old TurboK
55 Tap 2904
55 FMJ 2773
75 Horn 2500
16 Green mountain mid unsurpressed new barrel
55 Tap 2929
55 fmj 2824
75 Horn 2511
18 WOA 3 gun interm gas w/YHM Turbok
55 Tap 3100
55 fmj 2960
75 Horn 2643
My TAP load is a 55 vmax with 24.7 Benchmark
My 55 Hornady FMJ is 25 XBR for matches
75 Hornady is over 24 varget or 26 CFE 223.
That’s much more in line with expected results.
Looks like 12.5 is kind of a sweet spot for the heavier projectiles.
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joedirt199
04-21-24, 13:43
My 12.5 is my oldest barrel brand new being 18 and 16 with only a few sighters rounds through.
Looks like 12.5 is kind of a sweet spot for the heavier projectiles.
Sent from my iPhone using Tapatalk Pro Velocity loss/gain per inch of change steepens under 12.5”. It is moderate between 12.5” and 16”, and fairly flat 16”- 24” or so. As we look at medium length barrels like 13.5” or 14.5”, an inch in either direction makes very little or no difference, but down in the 10.3” region, an inch can be a big change in noise, flash, trajectory/ballistics, reliability, and silencer wear. In the opposite extreme, there is almost no difference between an 18” and 20” barrel, in practical terms. As in, you really need a chrono to see the difference.
Handling difference between a 12.5” and 10.3” is nil.
In my view of general purpose rifles, which is merely my opinion, the sweet spots are:
11.5”-14.5” for silencers (Mk18/M4 role),
12.5”-18” for A2 flash hiders(M4/M16 role),
16”-20” for light support weapons (M27/M38 roles).
Velocity loss/gain per inch of change steepens under 12.5”. It is moderate between 12.5” and 16”, and fairly flat 16”- 24” or so. As we look at medium length barrels like 13.5” or 14.5”, an inch in either direction makes very little or no difference, but down in the 10.3” region, an inch can be a big change in noise, flash, trajectory/ballistics, reliability, and silencer wear. In the opposite extreme, there is almost no difference between an 18” and 20” barrel, in practical terms. As in, you really need a chrono to see the difference.
Handling difference between a 12.5” and 10.3” is nil.
In my view of general purpose rifles, which is merely my opinion, the sweet spots are:
11.5”-14.5” for silencers (Mk18/M4 role),
12.5”-18” for A2 flash hiders(M4/M16 role),
16”-20” for light support weapons (M27/M38 roles).
I'm very fond of the 12.5-13.9" with a K-can.
I very much regret selling my 12" but I'm loving my 13.7".
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I thought I had a spare gas block to assemble the 13.5”, but I don’t. While we wait on that:
81*F
12.5” Hodge/Velos
Federal XM855
2819 fps
39 es
13.6 sd
12.5” BCM Kino/Turbo K
XM855
2825 fps
69 es
20.3 sd
12.5” Criterion Core/.264 MG7k
XM855
2824 fps
31 es
9.5 sd
69gr Norma .223
2620 fps
38 es
11.1 sd
90*F
13.5” Mos Tek 5.56 Mid
Unsuppressed
XM193 Fed
Av 2970
Es 80
Sd 20.6
XM855 Fed
Av 2870
Es 42
Sd 12.9
Norma 69
Av 2651
Es 41
Sd 14
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