Any time a change is made ,ammo,springs weight ect: the gun will react differently. You might be used to the way it was set up before, now you have to relearn. Timing is everything. You can not stop recoil.
Check your brass for excessive bulging. Even if you only have a few in the mag. The combination of a rimed case and a bulge can cause havoc. Two bulged rounds back to back is a recipe for failure.
Are any of you guys using 38 super with MBX mags? I am having an open STI built but plan on running super not SC. Any issues I should know about or are am I Good to go. Thanks