Odd Phenomenon - 38 Special target rounds

I would have thunked that if the barrel is getting hot, the inner diameter would increase, not decrease--maybe even allowing some pressure blow-by. Hotter the barrel, the bigger diameter, the more gasses blowing by the bullet, thus a slower FPS.

I'd say scrub that barrel CLEAN with some copper solvent, and then try a slower-buring powder.
 
UncleLoodis,

If you read the second sentence of my post above, you'll see it does expand, but only by about two tenths of a thousandth of an inch in going from room temperature to scalding hot (I used 75° increasing to 165°F). The actual linear temperature coefficient of 4130 steel is about 6.2 parts per million per degree F°, so I used that. It's not enough difference to start a significant gas leak around a copper-covered bullet. I was assuming that, like a cast bullet it would start about 0.001" oversize, but double-checking, I see it does not. Still, copper doesn't gas cut easily like lead, so it should be OK.
 
Fire Lapping

It sounds like I should consider fire lapping my barrel.

Something I need to look into. With the plating issue aside, if it reduces leading, that would be a plus too.
 
I still think upping the charge will resolve this issue although it won't fit you're objective. Generally very light loads are a no-no because it makes it likely to be gun specific. The thing with competition it can get to be cost is a no issue, issue.
 
Here's the rub: Even if we get to the bottom of the problem, then what? I need those bullets, operating at my design velocities, running through that specific gun. They're purposed for competition. The concern is failing to make chrono if I get called to test after there's a bunch of barrel buildup.
Click to expand...

Well, with the results you are seeing I would not trust them at all. If you could find the problem, the knowledge would help you find a solution.

Another revolver (or more) would show you if it is an "across the board" failure or just the one firearm.

I never bothered loading to the 105 PF for SSR but to make 125 PF out of my 4" 686 I have used:
158 grain Berrys RN @ 1.525" OAL with
3.3g N310
4.4 Clays
4.2 of tight group
6.1 of HS-6
4.4 Bullseye (the one that feels the best to me).

All are just over 800fps out of a 4" 686 using 38 spl brass (do not use this data for a 38 spl revolver).
 
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