"In the work-up, 14.5 gr was the last point that did not cause the cases to bulge at the base, and gave around 1100f/sec with a 158gr XTP. 15.0 gr bulged the case heads slightly, 15.6 such that extraction was difficult."
OK, a couple of problems with that, I think...
1. I think you have a gun issue, not a powder issue.
2. Your powder charges with H110 are too light.
Hodgdon's website shows, for 158-gr. XTPs, a MINIMUM load of 15 grains and a maximum load of 16.7.
The warnings with H110/WW296 has, for many years, been that you should never drop below Winchester's (or Hodgdon since they took it over) recommendations.
I routinely use use 22 grains (MAX LOAD!) of WW 296 behind a 125-gr. bullet, and 16.5 grains of 296 behind a 158-gr. bullet in my two N frame .357s and I have never had anything even remotely resembling what you're describing.
I'm thinking that you've got a revolver with oversized chambers.
Regarding the muzzle blast, yes, that will happen with heavy charges of just about any slow burning powder.
Regarding your measure, my bad, I didn't realize you were talking about the rotary drum measure -- I was thinking one of the Auto Disk models.
Yes, a fine-grain powder like 296/H110 can do that.
If you think H110 is fine, I'd suggest that you never try AA 7... It's like talc.