Same load, similar length barrel, significant difference in muzzle velocity

[sk8242]

Hi,

 

New to the forum and to reloading and was hoping to get some thoughts on an observation.

 

I made up a load ladder with the following with the intent of starting to load for 9mm minor:

 

-147gr TC poly coated lead bullets from DG Bullets (.356" diameter)

-mixed brass, full length resize, untrimmed

-Federal Match SPP

-Case mouth flare to ~0.382"

-2.8 to 3.4 grains of Shooters World Cleanshot

-Loaded to an OAL of ~1.135"

-Crimped to ~0.378-0.379" with a Lee factory crimp die

-All cartridges loaded on a Lee Classic Turret press, with Lee dies

-Chrono'd using a Labradar chronograph -- target @ 25 yards, muzzle @ 6" lateral offset from the radar

-32F ambient temp

-10 shot average for each powder charge -- STDEV charted as error bars and generally very consistent measurements shot to shot

-Tested out of a Beretta LTT Elite Centurion (4.25" barrel) and an M&P 2.0 Metal (4.25" barrel)

-As a baseline control, I checked average velocities out of 2 factory loads -- 150gr Federal Syntech, and 147gr American Eagle -- I saw the same 40-50fps difference between the two same guns

 

Very quickly during the testing it became clear that the M&P was sending projectiles on average 40-50fps faster than the Beretta. From my limited research, it seems that this is pretty common. But it's still a pretty significant difference when considering the overall muzzle velocity of the projectiles and the fact that I'm trying to load to as low of a PF as possible while still taking into account normal variations from cartridge to cartridge. Looking at the data, it would suggest that I can load as much as 0.4 grains less if shooting out of the M&P and still make 130 PF (under these testing conditions), while the Beretta requires that much more propellant. While doing plunk tests to determine what OAL I should start loading at, I noticed that the Beretta chamber was essentially at the max SAAMI spec of 1.169", while the M&P had a slightly shorter leade, closer to 1.145" or 1.150".

 

I'd be interested in hearing from others regarding their experience, if any, with a similar situation. Did you end up changing propellants, or just load for the slower barrel? Would the OAL cause this effect this in any way, or is it primarily dependent on barrel/chamber dimension variations from manufacturer to manufacturer?

 

Please see attached images for the graphed data. Note a velocity of 851fps is the minimum to make PF with a 147gr projectile.

 

 

?

 

 

 

 

 

 

 

Edited December 16, 2022 by sk8242

[Alaskapopo]

Barrels are different I have a 5 inch 357 that has slower velocity than my 3 inch barrel with the same loads 

[SteelCityShooter]

If you are loading to different cartridge lengths for the two guns then the shorter LOA cartridges will develop more pressure for the same powder charge due to the smaller net case capacity.   That could account for the velocity difference.   That said, as mentioned above, every barrel is a world unto itself and some are faster than others.

 

I've noticed that my two M&P2.0s (a 5" Pro and a 4.25" Metal Frame) both have short chambers and require an LOA of 1.105 with a 125 gr Blue RN to "plunk" properly.  

[superdude]

It's not unusual to see barrels of the same length produce different speeds, and for shorter barrels to be faster than longer barrels.

 

https://www.ssusa.org/articles/2021/8/16/pistol-barrel-length-and-velocity

[Farmer]

Try loading to the shorter length for the S&W and see how they work in the Beretta. I’ve done tests where I loaded rounds at .010, .020 and .030 from the lands and many times the .020 will be the fastest. 

[HesedTech]

21 hours ago, sk8242 said:

But it's still a pretty significant difference when considering the overall muzzle velocity of the projectiles and the fact that I'm trying to load to as low of a PF as possible while still taking into account normal variations from cartridge to cartridge.

Not a significant difference at all. Barrel length is only part of the equation, rifling, barrel diameter, chamber, throat and probably other things all effect the velocity. If I load for 130 PF in my CZ Shadow 2 it will barely make PF in similar length Tanfoglio. Also the CZ using the same load is significantly more accurate than the Tanfoglio.

 

If you want to build just one load then do it for the slowest barrel you will be shooting and then not worry about the difference. In the heat of a stage the last thing you will notice is a 5 PF difference.

 

Honestly I load to an average PF of 133 to cover variations and not worry about Chrono stage.

[GMM50]

Not exactly what you're talking about, but consider the following.

 

We manufacturer coated bullets.  We use Hi Performance bullet coating.  Out bullets are brinell 12.

When comparing lubed bullets to coated bullets, we consistently see velocities in the coated bullets higher than the lubed.

Also, for about 10 to 20 rounds, the coated bullets keep increasing in velocity.

Our only explanation is that the coated bullets are cleaning the barrels.

 

So be sure you take enough samples to make sure your setup has stabilized.

 

[Cuz]

I see the same kind of difference between my gen3 and gen5 Glocks. The gen5 barrels are considerably slower with the same ammo. 

[Scotty_JR]

I've got a friend with a fullsize LTT that shows similar results. His barrel is considerably slower as well. He has to run a few tenths over max of Clean Shot to make 135PF. 

[Farmer]

On 12/17/2022 at 8:09 AM, HesedTech said:

If I load for 130 PF in my CZ Shadow 2 it will barely make PF in similar length Tanfoglio. Also the CZ using the same load is significantly more accurate than the Tanfoglio.

Found the same thing between my brothers 4.5”Witness in 10mm and my 3.8” XDM 10mm. The XDM even though gives up .7” of bbl it’s still faster. Actually it’s only 50-70 fps slower than my 5.25 bbl. 

[shred]

I've had 3 otherwise-identical Bar-Sto barrels in the same Open gun over the years.  All of them have been more than 50 FPS different from each other with the same loads.  Barrels vary, it is what it is.  

[Laughing_jackal]

I saw massive differences comparing a Walther PPQ to a Glock.  In that case, I learned that the Walther PPQ had a stepped chamber, and I attributed the velocity difference to that.  In my situation, to keep things simple between guns, I just ran the same load for both guns as it was.

 

In the precision rifle game, we've definitely seen "Fast" barrels and "Slow" barrels come from the same barrel maker, cut with the same reamer, same length, same twist rate, etc.  

[ysrracer]

Name: 9mm: 147gr: Cleanshot 3.5gr: Mixed Case: OAL 1.140
Notes: Para 1911 5"
Shots: 7
Average: 901 ft/s
SD: 12 ft/s
Min: 874 ft/s
Max: 912 ft/s
Spread: 38 ft/s
Power Factor Average: 132
Power Factor Low: 128
Power Factor High: 134
Barometric Pressure: 30 in Hg
Temperature: 68 F
Weight: 147.0 gr.
Powder: Cleanshot 3.5gr
Case: Mixed
Primer: Rem SPP
Bullet: 147gr
Gun: Para 5" 1911

[Khaot1c]

If you need more data to show how important it is to test EVERY barrel you're going to go to a major match with...

 

I have 4 KKM barrels for my SIg 320 Legions.

Each will post slightly different Average Velocity, Extreme Spread, and Standard Deviation.

Even though they are the "same" barrel. Probably manufactured within a close timeframe of one another since I ordered (and received) all four in the same internet order from KKM.

 

[ysrracer]

On 12/16/2022 at 10:58 AM, sk8242 said:

Very quickly during the testing it became clear that the M&P was sending projectiles on average 40-50fps faster than the Beretta

 

Yes.

[Bakerjd]

Yeah pretty normal.

[floater]

I have a Beretta 92 that is the slowest barrel I have.