Gun getting slower?

[John Z Sr]

Put some of my standard loads through the chrono yesterday, getting ready for SC section match this weekend. From my 4" 625, 4.1 grs. of Clays has always given me a power factor of 168-170. Got chronoed at 6 big matches last year, plus my own chrono and always made it. Yesterday I only made 159, and everything has been exactly the same with the load. Could my barrel be getting worn and that is causing the drop in velocity? I do have about 10,000 rounds through the gun since last August. Any input from those with more experience would be appreciated.

[cooper_999]

Put some of my standard loads through the chrono yesterday, getting ready for SC section match this weekend. From my 4" 625, 4.1 grs. of Clays has always given me a power factor of 168-170. Got chronoed at 6 big matches last year, plus my own chrono and always made it. Yesterday I only made 159, and everything has been exactly the same with the load. Could my barrel be getting worn and that is causing the drop in velocity? I do have about 10,000 rounds through the gun since last August. Any input from those with more experience would be appreciated.

from my experience, the cylinder gap and the cylinder holes have big influence on the velocity of a load. My old 586 has had a nice cylinder/barrel gap but worn cylinder holes - due to that poor velocity. Another reason could be a slight change in powder recipe from charge to charge. I´ve measured often differences in velocity with the same components by change from powder can to powder can. Since I got chronoed minor one time, because I´ve not checked a load after changing the can, I chrono before every match now.

DVC,

Sascha

[Boats]

Gun aside, Powder changes lot to lot and will also change considerably ambient temp changes. Different bullets have effect too. some slip down the bore easy others have more resitance & less velocity for the same powder charge.

Working on the edge of PF best to Crono the exact load.

Boats

[Gregg K]

John

Were there no other changes? Changes of brand and style of bullet even of the same weight will cause a change of that much like going from lead to hard jacket or even from one lead bullet to another that has a concave base instead of flat. A change in seating depth can make big differences too. As Sascha mentioned, powder can change from lot to lot. I get my powder in a 25 lb keg to avoid changes. It could be several small things stacking to give you the change, it's not likely that you have wore the gun that much in 10K.

[John Z Sr]

That's what I figured, thanks guys. Good thing that I'm self-unemployed for now, that gives me the time today to load some new ones up and hit the range with the chrono. Guess I might as well get some more practice in while I'm there.

[cooper_999]

I get my powder in a 25 lb keg to avoid changes.

You are lucky! I can only buy 500g / 454g cans in Germany All countries around us have 2kg cans (Vihtavoury/Kemira) but we are not allowed to buy them. Due to that, I buy some small cans and mix them, to get a constant lot for a longer time.

[Carmoney]

A couple thoughts:

1. Smokeless powders are actually incredibly consistent from lot to lot, and from year to year. Several years ago I defended a personal injury burn case involving smokeless powder, and had the opportunity to interview and depose a product manager who spent 40+ years at the old Hercules plant. He described the processes used to maintain consistency, and its pretty incredible. There is no significant difference between the Bullseye powder made today and the Bullseye powder made in the late 1800s.

2. Ordinarily, cylinder-to-barrel gap does not increase as the gun wears--if anything, the gap decreases as the end of the yoke barrel and the internal seating surface in the cylinder slowly wear against each other, allowing the cylinder to move forward.

3. 10K rounds of relatively mild .45 ACP ammo is not enough to have any significant impact on barrel, cylinder, or forcing cone dimensions.

I think it's more likely that the issue is caused by chronograph variability (e.g. lighting, technique, etc.), an incremental change in the load, or temperature variation......in that order.

[snertley]

CHeck your cylinder to barrel gap, when I got my 2nd 610 it would chrono almost 100 fps faster then my old 610. The I found the gap was way too tight. Gary streched my crain and now the is no difference in volocity between the two guns. You may have too much gap.

Edited April 5, 2010 by snertley

[Carmoney]

It may have too much cylinder gap, but if so, it's been that way all along. It certainly doesn't explain a change in velocity. Cylinder gap doesn't increase over time, it only decreases. And the only way to reduce cylinder gap (without creating unacceptable end-shake, that is) is to refit the barrel, setting it back a thread.

Edited April 5, 2010 by Carmoney

[Round_Gun_Shooter]

That's what I figured, thanks guys. Good thing that I'm self-unemployed for now, that gives me the time today to load some new ones up and hit the range with the chrono. Guess I might as well get some more practice in while I'm there.

What are you using for bullets?

[John Z Sr]

Found the problem. Loaded up some "Precision Delta" 230 fmj's (my normal bullet) and they were 733.75 fps for a 168.8 PF, just like they always are, and then shot some more of the "slow" ones, "Montana Gold" 230 fmj, they came in at 696.8 fps for a 160.3 PF. Everything was the same except for the bullet brand, heard MG are harder and maybe that made the difference. Glad I just bought a box of Precision Delta's . Hope this helps someone else out and thanks for the feedback.

[KPIC24]

John the MG are a lot harder than the PD

[Round_Gun_Shooter]

Found the problem. Loaded up some "Precision Delta" 230 fmj's (my normal bullet) and they were 733.75 fps for a 168.8 PF, just like they always are, and then shot some more of the "slow" ones, "Montana Gold" 230 fmj, they came in at 696.8 fps for a 160.3 PF. Everything was the same except for the bullet brand, heard MG are harder and maybe that made the difference. Glad I just bought a box of Precision Delta's . Hope this helps someone else out and thanks for the feedback.

That's kinda why I asked. Glad you figured it out.

You might want to try Donny Miculek's Bayou Bullets