Rifling affects velocity

[godan]

To measure the effect of rifling on velocity, I chronographed three factory loads in both a CW40 with conventional rifling and a P40 with polygonal rifling. The altitude of the range is 5040 ft. Temperature was 38F. Velocity is the average of three rounds. ME is calculated from the Georgia Arms website tool. All rounds are 180 grains.

CW40: Privi Partizan JHP, 790 fps, 249.5 fpe. Win. White Box JHP, 883 fps, 311.7 fpe. Underwood TMJ, 1033 fps, 426.6 fpe.

P40: Privi Partizan JHP, 797 fps, 253.9 fpe. Win. White Box JHP, 958 fps, 366.9 fpe. Underwood TMJ, 1065 fps, 463.4 fpe.

This is a small sample, measuring only rounds of interest to me, but the tendency is clear.

I also chronographed some 9mm in a PM9. The hottest round, also the most accurate at 50 yards, was the Underwood 115 grain JHP. Its velocity was 1341 fps. Its muzzle energy was 459.3 fpe - only 4.1 fpe less than the best 180 grain .40, above...and the barrel is a half inch shorter.

[AIRret]

Holy smokes batman that's food for thought.

[muggsy]

You need to test more than three rounds in each barrel to get a definitive answer. Velocity can vary by the amount that you stated in the same barrel. A variance of 30 fps or more is not at all unusual. You would need to get an average of several ten shot strings from multiple barrels to learn any thing meaningful. I don't think that anyone who was shot could tell the difference in velocity. Just sayin.

[kerby9mm]

I guess this proves the polygonal barrels get a little more velocity even though the bad guy wouldn't be able to tell the difference.

[godan]

I guess this proves the polygonal barrels get a little more velocity even though the bad guy wouldn't be able to tell the difference.

That is the essential point - there is a clear difference, but probably not enough to matter in real life. Chronographing rounds tuned for handgun silhouette involves much larger samples, but in this instance, I doubt that more specificity would alter the general outcome. Although, I would be delighted to learn the results of a more complete test if anybody does one.

I was surprised by the performance of the Underwood 115 grain JHP in the short PM9 barrel. After breaking the gun in, I looked for 50 yard accuracy with trusted 115 grain JHP +P's, including Underwood, Speer Gold Dot, Federal 9BPLE, Corbon JHP and Corbon DPX. The Underwood was tightest and most easily adjusted to POA, and this morning I discovered its excellent muzzle energy.

[unclenunzie]

I also chronographed some 9mm in a PM9. The hottest round, also the most accurate at 50 yards, was the Underwood 115 grain JHP. Its velocity was 1341 fps. Its muzzle energy was 459.3 fpe - only 4.1 fpe less than the best 180 grain .40, above...and the barrel is a half inch shorter.

That is approaching .357 magnum levels out of a 3" 9mm! :eek::D

I'm not so sure I'd want to run very many of those in mine :)

[godan]

That is approaching .357 magnum levels out of a 3" 9mm! :eek::D

I'm not so sure I'd want to run very many of those in mine :)

Yes, it does demand attention, but the I think the pistol can handle the fifty per year I intend to shoot. Practice rounds are a mild 9mm load I developed for GSSF matches.

Underwood also makes a .40 SW round that pushes a 135 grain bullet at 1500 fps. That is 674.6 fpe. I tried it in a CW40 and decided it would be just too much for the pistol even in small doses.

[CJB]

This is a small sample, measuring only rounds of interest to me, but the tendency is clear.

Very hard to draw any conclusion.

The reason being, is there is no sampling of barrels. You have one sample of each type, so the only conclusion you can make is for those "specific" barrels.

If you took a larger sampling, say five of each barrel, and put ten rounds of whatever ammo... through each barrel, then you'd begin to see a trend.

There is a good deal of variation from barrel to barrel. Chambering length, chamber diameter, rifling lead-in, the surface finish of the rifling, the rifling itself, bore diameter, any constriction of anti-constriction in the bore or rifling.... you name it, it all matters.

[godan]

Very hard to draw any conclusion.

The reason being, is there is no sampling of barrels. You have one sample of each type, so the only conclusion you can make is for those "specific" barrels.

If you took a larger sampling, say five of each barrel, and put ten rounds of whatever ammo... through each barrel, then you'd begin to see a trend.

There is a good deal of variation from barrel to barrel. Chambering length, chamber diameter, rifling lead-in, the surface finish of the rifling, the rifling itself, bore diameter, any constriction of anti-constriction in the bore or rifling.... you name it, it all matters.

I appreciate your reservations. Ten years of fine tuning loads for metallic silhouette competition made me familiar with the matters you mention. For the purposes of identifying differences between two specific pistols I own, with three commercial rounds I know well, I am happy enough with the conclusion I can draw. However, if someone can report the results of a more comprehensive test, I will be grateful to learn of them.

[kahrsport]

from the reading i have read in barrel riffling... poly vs conv given same barrel lenght there shouldn't be any real muzzle velocity... now that being said i should point out i know not the physic aspect of any of this... just reporting from my own readings... yours is a very special case in study and i don't doubt you but for general purposes that huge of a difference could only come from different lenght barrels say 3.5" vs 7"...

but i am curious about one thing if any smart member can chime in... so polygonal rifling makes it harder for the forensic crew to be able to say which bullet can be matched up to which gun right? ie poly barrel leaves very little markings on bullet?