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.
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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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would the extra barrel length from the 13.7 inch , be better for those longer range shots then the 12.5 inch ?
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.
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.
I’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:
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.
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.
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.
MosTek.
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.
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.