Your problem is the bullet isn't sealing the cylinders of the 624. Been there done that. No seal ='s no pressure/no complete burn. Then the bullets skid when hitting the forcing cone causing leading and poor accuracy.

If you look at the picture of the 624 I posted above you will see that there's bullets in that picture. They are 220gr hbwc's cast/sized to .432". If you look closely you will see that those .432" bullets are loaded:
flush
crimped in the top lube groove
crimped in the bottom lube groove

I was seating those bullets at different depths looks for accuracy/testing loads. Accuracy ='s x-ring on a nra 25yd target or 1 1/2" 10-shot groups @ 25yds.

I found the accuracy I was looking for with that 220gr hbwc crimped in the bottom lube groove/ over 1/2" of that .432" bullet sticking out of the 44spl case. The bullet had to go that far to fill/seal/start strait in the cylinders & accuracy was excellent.

You never said if you cast your own bullets or not. A custom mold from Mihec (he's in europe/slovania)
MP MOLDS - Bullet molds
or a mold from neo molds here in the states
N.O.E. Bullet Molds Main Site
Will have you casting making .432/.433" bullets.

Or if you don't cast buy some .430" un-lubed bullets and for under $100 you could be powdercoating your own bullets. Bumping them up to .432".

The 624 isn't going to have any real accuracy until you start feeding it .432" bullets. Then the groups will shrink and the un-burnt powder will be a thing of the past.

I shot that 624 for over a decade in bullseye matches. Before I bought the custom molds that cast oversized bullets I swaged my own .432" bullets

Truly powder coating is the way to go with lead bullets. I use shoot a 686 for bullseye anymore loaded with 38spl's. Here's what the 686 looks like after a 200 round range session.


Not hand picked/cherry picked targets by any means. These are the test targets used when looking for 50ft bullseye loads from that 686. 6-shot bugholes using powder coated bullets.


I own a beater 629 and a bunch of molds for the 44cal's and wanted a plinking load. I tested 6 different bullets and 7 different powders using the traditional lube/sized/cast bullets and found 3 loads that would do mgb @ 25yds.
mgb ='s minute of golf or 1 1/2" @ 25yds/nra bullseye
I re-tested using the same bullets and powders/loads. This time I powder coated the bullets instead. The end result was 13 loads that would do 1 1/2" @ 25yds.

Same bullets/same alloy/same powder/same reloading dies/same 629. The only difference was traditional lube vs pc. The end result was 13 vs 3/the 13 targets from the test loads using pc'd bullets.


Order a bunch of bullets cast from 10bhn to 12bhn alloy that are not lubed or sized. Power coat them/load them/hit the loud button & enjoy. You'll be shooting bugholes in the targets.