Your little SP-101 will digest all sorts of .38's just fine for target use including wadcutters. I tried 158 gr .357's and found them to be hard on the hands (like hitting a stinger with a baseball bat). 125's are probably easier. Like a dummy I sold my SP-101 and I'm sorry. Only good thing was I kept it in the family by selling it to my son, who put Crimson Trace grips on it. He hasn't repeated my mistake so I guess he learned something from the old man.
When you go to buy ammo ask for a run down of the selection and price. American Eagle .357's are about $13 a box up here in NH, and they're perfectly good for practice. 125 Grain hollow points are $50 a box. Same with .38's. Fully jacketed .38's are okay for practice, though you would want jacketed hollow points for defense.
Compare the prices of the practice stuff and the defense stuff and you will see a big difference. Don't just say I want .357's. I try to stay away from the lead bullets and go for the jacketed stuff. Some of the softer lead bullets will foul up the barrel pretty quickly.
By the way, I found that the Wal-Mart here has the best prices on .38 + p's. Maybe you should check them.
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