Some time back I bought a Remington RP45, with all of the bad reviews that gun got, I just had to try one out. I have had the gun for over a year and can find nothing wrong with it. It is accurate with cast bullets, will fed any bullet shape from full SWC to round balls. I was happy enough with the .45 that I thought I should get a 9mm as well. Not being one to rush into things, the RP9 purchase went on the "back burner". One day when I was cruising around the CDNN page looking at magazines I found an ad for a RP9 slide barrel and magazine all for $39.00, looked like a bargain to me, so I ordered the "kit".
A few days later the parts arrived, the slide came with and extractor and firing pin block in place. I borrowed the missing parts from my RP 45, put the 9mm slide on the .45 frame, loaded up the 9mm magazine and went off to try it out. It worked just fine.
I called the Remington service department and ordered the missing parts for $50.00 and change. Now I have two complete slides, to change calibre I swap slides and magazines. When I was trying out the 9mm configuration, I was using some cast bullet reloads, the Lee 125 gr. RNFP bullet over 5 gr. of Unique, these loads produced 1200fps+ average according to my chronograph.
A fun project, kind of like getting another gun for less than $100.00