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.