The size of the paint depends on which particular model of RAP4 you are using. Some do use .43 caliber paint, but some use the standard .68 as well.
For detents, you could always drill holes in the sides, and use detents that are like those on an autococker. The detents are basically a small screw with a ball and spring mechanism in it. The ball holds the paint in place, but springs back as the bolt slides past. The detents just simply screw into the side of the marker.
But this still doesn't solve the issue of getting the right pressure on your paint. You need some way to funnel them to the breech, or else they will jam. I think RAP4 magazines use a coiled track with a spring driven mechanism. It keeps the paint in a single line which makes jamming less of a problem.
2003 ICD BKO w/ 45/4.5k, Ricochet Apache
'98 r/f Autococker w/ 45/4.5k, J&J Edge kit (14"), Ricochet 2KX
PCS US-5 Mech. w/ 48/3k, J&J Edge kit (10"), cyclone feed, JCS folding voodoo stock with RVA
Kingman Hammer w/ 13/3k, J&J Edge kit (14")
Projects in the Works:
'99 r/f Autococker w/ 45/4.5k, J&J Edge kit (14"), and THE CYCLONE!!!