I have been using 3-d and Hornady 148 gr. lead double and single ended w.c. that I got probably about 10-15 years ago. I recently went to my local gun shop and got some .38 / .357 bullets by ProofMark and they slid into the barrel of my shell if you tapped them and so the first one I tried when it went up to be crimped slid into the barrel and the crimp applied. I have not gotten calipers to see the diam., but what is the correct diam. for a .38 spcl bullet head? Are they different? I saw some Hornadys for .357 bullets, .357 and for .38s, .358. I guess I will have to either alter my setup for my dies, or check the diam. with calipers and get the same. I thought all would be the same diam.? Would .001 make that much of a difference?
"...heads...", "... they slid into the barrel of my shell..." A little free advice. If I were you, I would learn the correct terms for the cartridge components to escape criticism by other board members. "Heads" are bullets. "Shells", unless talking about shotgun, are cartridge cases, "barrel" of a case, is the case neck.
If .357 and .358 bullets "slide" into the .38 Special cases, the cases have not been sized to the correct size.
Either .357 or .358 diameter lead wadcutters should work in a .38 Special gun.