9mm velocity and barrel length

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greyling22

greyling22

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I have a load that is subsonic right now in my handgun. 4.75" barrel, 1000fps. and in a 16" barrel it does 1160. do you think it would stay subsonic in an 7.75" barrel?

load is 4gn WSF under a lee 125grn lrnfp.

also, what I don't know is if you lose velocity by using a blowback carbine vs a tilt barrel pistol, assuming the same barrel length.
 
I think the velocity can change from gun to gun, even with the same length barrel. I doubt a blow-back design will lose much, if any, velocity.

I would bet money the 7.75" barrel will be between the velocities you listed for the 4.75" and 16" barrel.
 
I have found in most 9mm loads going from 3" to a 5" picks up about 30-40fps or 15- 20fps an inch.
11.26" gained you a 160 fps of about 14.23 fps an inch, so going to 7.75 would probably gain you 40 to 60 fps.
 
I don't have a 7" barrel. I'm looking to sbr my cz scorpion. I have a 16" carbine, and they make an aftermarket 4.5" barrel, a factory 7.75" barrel, or I could chop my barrel to any length. If I use a 7.75" barrel I can use a cz factory pistol handguard, which would be cheaper than an aftermarket guard.
 
greyling22 said:
I have a load that is subsonic right now in my handgun. 4.75" barrel, 1000fps. and in a 16" barrel it does 1160. do you think it would stay subsonic in an 7.75" barrel?

load is 4gn WSF under a lee 125grn lrnfp.

also, what I don't know is if you lose velocity by using a blowback carbine vs a tilt barrel pistol, assuming the same barrel length.
Click to expand...

I have a couple of pretty established loads I run in 9mm that I recently had an opportunity to shoot over my buddies Labradar chrono. My primary 9mm pistol is a S&W M&P Pro 5" with an Apex barrel, my carbine is an AR9 with a 10.5" Green Mountain barrel.

Loads:
115gr HiTek coated - 5.6gr CFE Pistol - 1350 FPS from pistol, 1450 from carbine
147gr HiTek coated - 3.1gr TiteGroup - 925 FPS from pistol, 975 from carbine

In 5.5" of barrel, I didnt get as much increase as I thought I would to be honest.

I was quite frankly shocked at the 115gr data, as 1350 FPS from a pistol is smoking fast, and 1450 is well, faster. Im not seeing any case issues, and the gun is not getting beat up, so Ill continue to run it, and its very accurate. The velocity gains seem low, as CFE Pistol is a moderately slow powder, so I was surprised at the higher pistol velocities, and lower than I suspected carbine velocities gain. Even still I gained about 20 FPS per inch, and maybe I might see 1500 from a 16" barrel, maybe. The 147gr data was about where I figured it, only picking up 50 FPS in 5.5" of barrel, still easily subsonic in the carbine. Im willing to bet that TiteGroup is just running out of gas in that 10.5" barrel, and in a longer barrel, Id probably see less gain per inch of extra barrel.

WSF is right in the middle of the pack for burn rate, but your velocity increases seem a little high. If you really want a subsonic load, you are either going to have to go to a faster burning powder or a heavier bullet or maybe both. You might be able to get the velocity on your pistol load down to say 950 with WSF, and then it very likely might be just barely subsonic in your carbine. There is a reason that 147s and fast powders are the go to for subsonic loadings, it just works. Unfortunately 124s are not a great choice for a subsonic load, but you could play with a faster burning powder to decrease the amount of velocity gain when going to the longer barrel.
 
again, the carbine barrel will be shortened. I'm just trying to pick a length to shorten it to. I'd like it long enough to retain some accuracy, but short enough to stay subsonic with my pet load. The scorpion with a 16" barrel was far more accurate out at 75 yards than the SBR mpx by buddy had (4.5" barrel)
 
greyling22 said:
again, the carbine barrel will be shortened. I'm just trying to pick a length to shorten it to. I'd like it long enough to retain some accuracy, but short enough to stay subsonic with my pet load. The scorpion with a 16" barrel was far more accurate out at 75 yards than the SBR mpx by buddy had (4.5" barrel)
Click to expand...

If you break it down to straight by the inches, your gaining about 15 FPS per inch from 5 to 16". The 7.75" barrel should net you about 1050(ish) with your current load.
 
Paul Harrel on YouTube did a video and discovered that a S&W M&P Compact with a 3.5" (+/-) was in a sweet spot of barrel lengths. It just seemed to be at the point where velocity increased by the greatest per inch. He compared it to a Beretta 92 and a shorter 9mm.

So the conclusion is that the increase in velocity follows a bell curve increasing as the barrel increases. The slope of the curve changes as it moves. Eventually the barrel length consumes the bullets energy and velocity will diminish. The manufactures have the resources to find the data points on the curve for their barrel & riffling design.
 
Obviously you reload, so whats the big deal?

If you dont like how the ammo shoots in whatever gun just tweak the load until it meets your velocity and/or accuracy requirements.

Build your ammo for the gun, not the other away around.
 
I fought my witness for a long time to get a lead 9mm load that shot well. I am reluctant to mess with that. Also, it is at the low end of the power spectrum, so I have some concerns about maintaining function at much lower power. But I bet I have room to wiggle, and it sounds like I wouldn't have to download much, if at all to make it work with a 7.75" barrel. I can chop the barrel and run the cz pistol handguard for about $130. That beats the heck out of the hbi micro conversion which is 260+shipping for a barrel and handguard.

varminator, you are right. Here is the backstory to my statement: I shot my scorpion carbine side by side with a 4" SBR sig mpx (both wearing the same can), and the scorpion was far more accurate. Since the shooters and ammo were the same, the most obvious conclusion was that the longer barrel made the difference. Thus, I'm working on the assumption that a 7 or 8" barrel would provide more accuracy than a 4". Now, I'm not scoping the thing and looking for 1" groups at 100yds, but with red dots, the carbine will currenly do 3" at 50 no problem. The mpx was more like 6-7" at 50, which was much worse than I would have expected. And there could be a lot more at play than just barrel length, but that was the most obvious culprit.
 
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greyling22 said:
again, the carbine barrel will be shortened. I'm just trying to pick a length to shorten it to. I'd like it long enough to retain some accuracy, but short enough to stay subsonic with my pet load. The scorpion with a 16" barrel was far more accurate out at 75 yards than the SBR mpx by buddy had (4.5" barrel)
Click to expand...
The problem here is, once you change barrels or modify a barrel it probably won't shoot that pet load the same way.

I suggest you pick the length you want and tweak the ammo to fit the barrel and desired velocity. Trying to accommodate any load by modifying the hardware is just the wrong way to go about it.
 
The longer barrel didnt cause better accuracy. Different guns have different accuracy potentials. Heck, different guns of the same model have different accuracy potentials. Guns with the same barrel length don't always shoot the same velocity.

The 7" inch barrel will probably still be subsonic, but not necessarily any more accurate.
 
Dudedog said:
I have found in most 9mm loads going from 3" to a 5" picks up about 30-40fps or 15- 20fps an inch.
11.26" gained you a 160 fps of about 14.23 fps an inch, so going to 7.75 would probably gain you 40 to 60 fps.
Click to expand...
Doesn’t the velocity improvement fall off with length? I mean less improvement for each succeeding unit of length after the powder is fully consumed.
 
I don't have a carbine so I can't say for what the gain would be for a 16" of longer barrel.
I was just giving a number for what I saw going from 3" to 4" to 5" in my 9mm pistols.

Greyling22 gained about 14 fps per inch going from a 4.75 in pistol to the 16" carbine.
In general I got a bit more than that going from 3" to 5" so yes it looks like it does fall off a bit.
 
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I believe the velocity improvement drops off with increasing length - diminishing returns.

Just for more data points, I worked up loads for a 16" carbine. When I shot those, I also shot them in a Witness Elite 4.75" pistol for comparison.

RMR 115 FMJ, seated to 1.100". Power Pistol powder, Winchester small pistol primer.
5.9gn - Carb 1440.0fps, Elite 1208.8fps
6.1gn - Carb 1491.0fps, Elite 1241.8fps
6.5gn - Carb 1523.8fps, Elite 1281.0fps
6.6gn - Carb 1534.6fps, Elite 1274.2fps

Xtreme 147 RN, seated 1.130
4.5gn - Carb 1152.2fps, Elite 962.2fps
4.6gn - Carb 1167.2fps, Elite 965.6fps
4.7gn - Carb 1189.8fps, Elite 979.6fps
4.8gn - Carb 1198.8fps, Elite 990.8fps
4.9gn - Carb 1229.2fps, Elite 1009.2fps

The 115gn 6.1gn loads are pretty accurate for a 9mm carbine, about 1.1" @ 50 yards, and a little less than 2.5" @ 100. I tried AA#7 and got a little more velocity, but the groups really opened up. My standard load for the carbine now is Power Pistol @ 6.1gn with the RMR 115 fmj. Just for fun, I routinely shoot them out to 200 and 300 yards, steel silhouettes. 200 is easy, 300 not so much. There is a lot of spin drift.

The short OAL is because the carbine has a short leade.
 
greyling22 said:
The ballistics by the inch guy has a bunch of data http://www.ballisticsbytheinch.com/9luger.html that shows that looks get barrels yield greaer velocities all the way out to 17", at least for most loads. It looks like roghly 8--11" gives the most efficiency. You get into diminishing returns after that.
Click to expand...
Interesting. It appears that the diminishing returns (for 9mm) start at a shorter barrel length for the heavier bullets. Less case capacity under a heavier bullet? I have to wonder how much the burn rate of the powders (not determined by those tests) affected the results.
 
Toprudder said:
Interesting. It appears that the diminishing returns (for 9mm) start at a shorter barrel length for the heavier bullets. Less case capacity under a heavier bullet? I have to wonder how much the burn rate of the powders (not determined by those tests) affected the results.
Click to expand...
Heavier bullet moves slower at same final energy. So it is not as far down the barrel when the powder is fully burned. Acceleration occurs earlier in the barrel.
 
greyling22 said:
I have a load that is subsonic right now in my handgun.
Load is 4gn WSF under a lee 125grn lrnfp.
Click to expand...

To me the biggest issue you have with using a single cartridge in 3 barrels is the lead bullet. To work correctly, lead bullets need to be sized very carefully to the barrel. "Fit is king" as they say. There's simply no way 3 barrels by different makers are going to be sized the exact same so that the bullet behaves the same way in each. Testing is required.

Lead is cheap, but lead is not always easy. Never confuse cheap with easy.
 
This thread has some interesting data on how 9mm velocities correlate to barrel length:

https://www.thehighroad.org/index.p...carbine-bullet-velocity.810127/#post-10358884

My data was specific to an SBR'd Scorpion pistol like yours.

luzyfuerza said:
My contribution is for bullets on the heavy side and with a barrel that is about half as long as your 16" carbine barrel; 147 grain Xtreme CPRN and Unique powder (similar to HS-6 and Power Pistol on the burn rate chart). I'm developing a load that is just subsonic out of my CZ Scorpion Evo pistol (soon to be SBR) and Omega can. I compared velocities through the Scorpion (7.75" barrel) with those from an XD service model (4" barrel).

Here's my data:

3.6 grains of Unique
XD: 851 fps, SD 25
Scorpion: 950 fps, SD 43

3.8 grains
XD: 884 fps, SD 17
Scorpion: 974 fps, SD 44

4.0 grains
XD: 913 fps, SD 11
Scorpion: 991 fps, SD 38

4.2 grains
XD: 947 fps, SD 10
Scorpion: 1032 fps, SD 19

Powder charges are as-dropped through my Dillon powder measure (+/- 0.1 grain even with tough-to-meter Unique) and an OAL of 1.162". Mixed brass. No accuracy data because I can't attach a buttstock to the Scorpion yet (haven't received the tax stamp).
Click to expand...
 
And here's more data comparing speeds through my XD 4" service model and SBR'd Scorpion pistol using various loads of Bullseye and 115 grain Xtreme CPRN bullets with mixed brass, an OAL of 1.135", and CCI 500 primers:

4.3 grains of Bullseye
XD: 1095 fps, SD 21
Scorpion: 1253 fps, SD 15

4.5 grains
XD: 1122/14
Scorpion: 1248/8

4.7 grains
XD: 1134/9
Scorpion: 1268/11

4.9 grains
XD: 1178/7
Scorpion: 1317/8

5.1 grains
XD: 1226/14
Scorpion: 1360/8

Note that 5.1 grains is Alliant's max charge for Bullseye behind a Speer 115 grain CPRN. Alliant gives a speed for this load as 1192 fps from a 4" barrel. My results are a little faster. YMMV.

For what its worth, best accuracy was with the 4.9 grain load: 2" at 15 yards with the XD, and 3/4" at 25 yards (0.40" @ 25 yards eliminating one flier) with the Scorpion (RDS, sandbag rest). Both were 5-shot groups. I haven't yet determined what this load will do with consistent brass.
 
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Here is a comparison that I made a few weeks ago.

Firearm Average Velocity
Scorpion - 1188
Hi-Power - 1076
S&W 9c - 973
The ammunition used were commercial FMJ reloads and were quite consistent.
 
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