I'm shooting a CPA 44 1/2 chambered for 28-30.I'm using a Darr 28cal bullet weighing 147grs with 12.2grs of 4759 with very good results.

I have both.  My RMC cases (from Dave Casey) came with a very small hole in the Small Pistol primer pocket.  That may be OK for extreme accuracy, but a standard size hole would make de-capping easier.  I use a 310 tool with a Universal De-capping chamber.

My load for 200 yards has been 11.6 grains 4227 with a 142 grain Hoch nose-pour bullet.  I think it might shoot more accurately with more powder, but it's a 44 action.

FWIW, the original UMC cases had LR (or maybe LP) primers.

I think the 28-30 was always shot with a smokeless priming charge.  Unless you want to clean between shots.  It is really a black-to-smokeless transition cartridge.

Nothing with the small pocket, both rifle and pistol are the same depth @ .117 - .123 

Large rifle and pistol pockets are different depths. Pistol is .117 - .123, rifle .125 - .132 

The above are SAAMI specs.

Frank

Waterman
Have you tried seating the primers through a piece of paper to set them out another two thou or so. I have a 44 1/2 from CPA and when using some primers which are a bit shorter than .127" this cures the problem. My rifle also has a screw under the lever which adjusts the mainspring tension. Having said this, too much mainspring tension causes the trigger to give problems, it's a bit of a balancing act, with my rifle at least, YMMV.
Mike.