Thank you. You have loaded the equivalent and it fits? I don't think that there is much difference between the Rem and AA hulls. I believe #1 Bismuth takes up more room than the smaller sizes. I really don't want to use a 3" hull. Not worth the adjustment from 2 3/4" for a relative few shells for hunting.
According to Hodgdon it is 8900 psi at 1300 fps.
1 1/4oz of Bi will take about the same space as 1 3/8 oz of lead. That is why I switch wads. The WinAA12R will handle it for sure. If you use that same wad for 1 1/4 oz of lead, you need to add at least one, and often 2 Cheerios under the shot to make it fill the wad enough for a decent crimp. That works just fine, but I prefer to avoid the cereal if possible.
I agree about the Rem hull and the WAA. I don't know much about the RP12 wad however. My loads are around 1250 fps and work well with #5s for ducks and pheasants. Occasionally, a really tight Canada will tempt me with a head shot. Never failed on them either, but I've only shot a few and do not recommend it.