Revolvers are good at making bullets back out if you don't crimp the bullet. Always crimp revolver loads. A bullet backing out can lock up your cylinder.
Just to expand on that thought, this happens when you a fire a heavy load with recoil-- the one you pull the trigger on works great, but the recoils pulls the other rounds in the other cylinders out a bit.
Also worth mentioning another big, BIG reason to crimp-- when shooting a semi-automatic, a solid crimp prevents a bullet from getting pushed further in to the case by accident by a feeding pistol. (also valid on a tube magazine fed rifle) A bullet getting pushed down in to a case can raise pressures exponentially.