Barrel velocity dropping with barrel wear?

[Canuck223]

Ok sports fans, stupid question of the day.

My friend and I were chronographing ammo today. His well worn but great condition SP01 was launching my ammo consistantly 50 fps or more slower than my STI GP6. While my gun consistantly printed 875-890fps, his was 825-845fps.

I was the shooter for both guns and there wasn't a cloud in the sky.

Prior to his purchase, this gun likely ate 20K of WWB ammo.

Does barrel wear affect velocity over time??

[G-ManBart]

Eventually wear will cause a drop in velocity, but that may not have been the cause of the difference you saw today.

Pick two identical guns off the production line, made one right after the other and you'll often see 50fps difference between them. It's kinda like magic, but it's very common to see. R,

[Tom S.]

I've yet to see a stupid question on this board, and yours is no exception!

G-manBart gave an accurate statement about it not being surprising to see a difference in velocity between two guns. Maybe I can supply the why. With revolvers, velocity can vary greatly from gun to gun if there is a difference in the cylinder face to barrel gap. Gas escapes here, and a larger gap would let more escape, causing lower velocity. In an automatic, while you have no gap to contend with, you have the sum total of the mass of the componets that have to be moved during functioning (slide, hammer, etc.), plus their springs and the friction created initiating cycling. How much gas pressure is bled off to initiate this movement effects how much pressure is left to impart velocity to the bullet.

Edited March 16, 2009 by Tom S.

[Canuck223]

I was suprised at the difference as our mutual friend recomended the load based on his experience with his SP01 and Shadow.

Oh well, I'll just have to custom load the boys ammo.

[Flatland Shooter]

Based on my experience:

I have a 9x21 Open gun that has over 75,000 rounds through it. I've kept detailed notes on chrono data, loads, etc from Day 1.

Every time I think the velocity has dropped due to a worn barrel, I'll pick up a new can of powder with a different lot number and find that the velocity has increased with age. Bottom line, based on the physics, a worn barrel should see a decreased drop in velocity but from a practical standpoint, it is negligible.

A while back I felt, also due to a worn barrel, the accuracy has deteriorated. But after some thought, it is probable that the accuracy has suffered not from the barrel wearing out, but other factors such as the cone wearing against the slide or the barrel no longer locking up as well as it did 50,000 rounds ago. (Failing eyesight is not even considered a factor.)

Bill

Edited March 16, 2009 by Flatland Shooter

[kevin c]

I had two new Schuemann bull bbls, purchased and fit into my Limited gun and its backup at around the same time. Right from day one there was a 50 fps difference between the two.

[dajarrel]

My son's .40 shoots about 50 fps faster than mine. Both are STI's although his is a couple of years newer than mine. As far as custom loading for your friends gun, you might do what I did. I loaded the rounds to make major (plus a bit abt 168-170) in my gun and he runs them in his gun at about 170-173pf. To tell the truth, you can shoot one gun and then the other and unless you are looking for it, you cannot tell the difference. You definitely will not notice the difference when the RO says, "standby" and the timer goes off.

fwiw

dj

ETA, this is based on my experience with my two guns. Your's may be different.

dj

Edited March 17, 2009 by dajarrel