Do you have to do anything to the pro mags to get them to function well?I have some of the old Pre Ban 15 round original Marlin Plastic ones. They made them in 25 rounders also.
Anything that fits the 795s will work also. I think Promag even makes or was making some 70 round Drums for the 795s that will work. I use the Pro Mag 25 rounders in my Papoose and my 99M1 and 99M2s also.
Now in steel that is differant.
EDIT: Sorry I was not thinking right. The steel 12 rounders I have fit my Old 56 Levermatic. So in steel I have really never seen one over 10 for the Papoose and 795. I guess.
If you are not completely stuck on Steel for some reason. I have had very good luck with the High Cap Promags.