First shot is slow

[Wyatt Smith]

The other day while working up a load for my 357 magnum while using 160 grain gas checked semi wad cutters with accurate No.9 the first shot of a string would always be about 100 fps slower than the rest.
After reloading the revolver, it would happen again.
I tried two different bullet styles and several different charge weights and had the same results. It’s a pity too because the subsequent shots were very close in velocity and quite accurate.
I don’t think it’s a chronograph issue as the recoil and report were noticeably less. Also I tried shooting some from the same chamber, so this eliminates a slow hole.
My W296 and IMR 4227 loads perform as they should.
Any thoughts?

 

[Grumpy gumpy]

Do you have a digital thermometer, take a temperature reading of the barrel/chamber before, during and after shooting, could be as simple as temperature sensitive powder and you could be right on the edge of its "sweet spot" Aside from that I have no idea.
Gumpy

 

[Wyatt Smith]

Do you have a digital thermometer, take a temperature reading of the barrel/chamber before, during and after shooting, could be as simple as temperature sensitive powder and you could be right on the edge of its "sweet spot" Aside from that I have no idea.
Gumpy

I may try it, but I can’t see it cooling off enough in the time it takes me to reload. Also they don’t keep getting faster, it levels off. For example one batch I tested the first round 1185 and the remaining 5 were all really close to 1300. If I excluded the first shot the extreme spread was only about 40 FPS. As soon as I got it reloaded, the same thing happened on the next cylinder full.

 

[Nhoro]

Are you firing the first round single action and then DA on the rest ? Maybe it is a light primer strike on the first or something similar.

 

[Ontario Hunter]

Try some 38 Special. See if you get the same anomaly.

 

[Wyatt Smith]

Are you firing the first round single action and then DA on the rest ? Maybe it is a light primer strike on the first or something similar.

Try some 38 Special. See if you get the same anomaly.

All shots are fires single action, but a light strike makes as much sense as anything.
My other 357 loads with two different powders are just fine.

 

[hoytcanon]

I recommend that you start with the second shot.

 

[Wyatt Smith]

I recommend that you start with the second shot.

That’s what my dad told me, “just shoot a warning shot.”

I tried some 41 magnum loads, it was the same story. I guess No. 9 is no good for lead bullets.

 

[Trogon]

Have your primary revolver loaded and ready with six rounds, and use another handgun to first fire a single shot? This is an odd situation for sure. What chronograph are you using?

 

[Wyatt Smith]

Have your primary revolver loaded and ready with six rounds, and use another handgun to first fire a single shot? This is an odd situation for sure. What chronograph are you using?

I will probably try this sometime just for the heck of it, but I doubt it helps as my loads with two others powders work as they always have.
It’s a Pro-Crono. I’d like to upgrade someday, but it works for now. I may drive down to my buddy’s and shoot a few through his chronograph just to see.

 

[Longwalker]

I was shooting my .357 magnum Win M92 carbine with some test loads the last couple days. I also experienced some slow velocity first shots. I also have no explanation. I was testing loads with Hodgdon Lil'gun powder and 180 gr. bullets, quite a different load. Mysterious.