Magnum loads with H110 spits from cylinder gap?

[55_grain]

I've loaded .357 mag rounds with H110, Win231, and WC820.
All 158-grain for the purposes of this discussion. Hardcast and JHP.
regular primers on the W231, mag primers on the others. Well crimped with LEE FCD.

I've loaded .44 mag rounds with H110, PowerPistol, and WC820.
All 240-grain, both hardcast lead and JHP's.
regular primers on the PP, mag primers on the others. Well crimped with LEE FCD.

All at appropriate loads per one or more published manuals, with mag velocities per my chrony.

Revolvers are both 6" with to-spec barrel-to-cylinder gaps.

Only the H110 "spits" powder out of the cylinder gaps, at the shooter and anyone too close to the left or right. It's kind of annoying

Why?

 

[EddieCoyle]

Because.

 

[*chris*]

Could it be since H110 is the slowest burning powder out of your group? my Winchester 296 - 357 mag loads spit a huge fireball.

http://www.lapua.com/upload/reloading/reloadingburningratechart2011.pdf

Chris

 

[EddieCoyle]

WC820 is about the same texture (fine ball) and burn rate as H110. I've seen the same thing with H110/296 and a few other powders.

 

[Gammon]

Maybe you need to use a roll crimp, if possible.

 

[55_grain]

4 days...I'd have expected a treatise on how many extra milliseconds for the bullet to fully engage the rifling with a slow burning powder vs the % of unburned H110 and the backpressure pushing the powder out the cylinder gap or something by now.