I bought factory shot shells in .38 spl and they worked fine. I bought shot capsules and loaded my own and they miserably failed. I couldn't keep the capsules tight in the cases and my rounds gained length from the recoil of the previous round and locked my cyl up. They were light rounds to. I obviously screwed it up.
I tried crimping them harder and cracked the capsules. I got discouraged and abandoned the idea.
I don't know what brand of capsules they were though, to long ago but they were green plastic and had a push in lid that went towards the powder if that helps any.
Not saying Speer's won't work, just my limited experience with the brand I had.