A while back I was making 3-1/2" 12 slug loads and asked if anyone knew what pressure the 12ga "brass" (actually steel) would stick. I said I would post if I ever found out. Well, it seems the magic # is around 20-21,000psi, a bit higher than my guess of 15-18k.
Having them tested was a big help in the right direction.
My favorite load tested in at 5848ftlbs energy @ 18,400psi. I imagine I could get the pressure down a few K without too much sacrifice in energy.

I bought a Damascus barreled shotgun for $20 to pressure test.

It looks like there is room for ~200 gr of H110 in a brass 12 ga shell.

I need to use a really long trigger string on this one.

He he.... sounds like fun.
One of my test shells had 2-1/2oz #9 shot with Alliant 2400, close in burn rate to your H110. I thought it would be too slow of a powder but it worked great! It launched at 1412fps and made 4835ftlbs @ only 12,100psi! I'm hoping the slow acceleration will not deform the shot, I'll pattern test soon.
All my other tests used Blue Dot or Steel and all those shells exceded the 14k SAAMI max. One was 25k, oops

One of you guys is going to make the Darwin awards this year....