[rg1]

Wiith your combination of powder and cases and 125 gr. bullets I would 1st recommend to check your sizing of the RP cases. The bullets need to have a tight grip in the case BEFORE crimping. Light bullet, lighter than normal charge of a powder that performs best at near maximum charges, can be a problem and cause squibs and stuck bullets IF the bullet is loose in the case. The primer by itself can start a bullet moving before the powder is fully ignited. If your expanding die is doing no expanding and you feel no resistance when expanding then your sizing die isn't sizing down enough. Check a seated bullet before crimping and if you can push it further into the case with your thumb or by pushing the bullet against the side of your bench. If you can move the bullet then it's not gripped tight enough in the brass. I've seen this several times at the range by my own .38 loads and also by others. I never got a stuck bullet but I had wild velocity variations by as much as 300 fps. I have seen others with stuck bullets and bullets blooping out and falling to the ground at 20 yards or less. RP brass CAN have thinner walls than some other .38 Special brands. Your combo 38/357 mag sizing die may not be sizing the RP brass down enough. I'd measure the expander plug also to make sure it isn't over size. You will see more problems like your experience with .38 Special than any other pistol caliber that is loaded. I got another .38 Special sizing die that would size down thin .38 cases and all problems disappeared. Check your case sizing. Possibly try another case brand. I like RP brass but some lots of RP brass seems to have thinner case walls. From your pics, I see no slight bulge on the outside or the case at the base of the bullet which "could" indicate that the bullet is not tight in the brass? How many firings with your case? Many firings can harden the brass and you could have more spring back when sizing? A crimp by itself is NOT enough to hold the bullet for reliable consistent ignition.