Mic the mouth of the cylinder and see what the factory dimensions for that particular revolver are. Odds are they are within spec and it's a problem with your ammo, but it won't hurt to double check.
If it is a .38 New Police (aka .38 S&W), a .38 Special won't fit - because a .38 S&W is a short cartridge. The .38 S&W is also a slightly different geometry round and is actually a hair bigger (won't fit into a .38 special chamber unfortunately).
I'd guess that you are belling your case mouth too much, possibly have some out of spec projectiles (not likely, but check them anyway) or are over crimping and putting a slight bulge in your brass just short of the crimp.
Oh, and I would love to run across a find like you did. This guy is jealous.