Since the 60's, target shooters have reported separating seating and crimping operations produces more accurate ammo. The reasons are not entirely clear. Certainly, without keeping them separate and if you have no crimp groove in a bullet you get some shaving because the bullet is still going in deeper while the crimp is formed. The nose of a soft bullet is probably bulged slightly by the conflict. But with a crimp groove I would think the combined seating and crimping would actually result in more consistent seating depth (lubricated lead bullets sometimes pop back up a little before crimping because of the air compressed inside during seating).
In any event, unless you have a match accurized pistol and are shooting near 90% or better on 50 yard conventional pistol targets, you probably won't really notice the accuracy difference. Only experimenting will tell you for sure, though.
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