It's been awhile since I thought about this type of question but You definitely do not want to roll crimp a semiauto case. It can cause headspace problems because a semiauto usually headspaces on the case mouth, whereas a revolver cartridge headspaces on the case rim. In answer to the possible pressure problem, I would suspect there is. A roll crimp bites into the side of the bullet, holding it in place for a longer duration and raising peak pressure.
When you taper crimp, the die firmly squeezes the case neck around the bullet and not into it. It can also affect accuracy. I agree with "10mmrules" and get that taper crimp die. Your cases will last longer and best of all your gun will last longer.
[This message has been edited by preacher (edited October 17, 1999).]