The reason I'm asking, is that it appears the heel mag release on the R-9 might be just about at the same level as the hole for the magazine release on the back of the P-7 PSP (not P7M8) magazine.
I thought it would be interesting to see if the P7 magazine would fit into -- and lock in the R-9.
I carry the P7 concealed routinely -- and with plans to make the R-9 as a pocket BUG, it would be convenient if an extra P7 magazine might just fit (and work) in the R-9.