I do not crimp unless necessary. What is necessary? In a semi-auto pistol, a lever action rifle, revolvers and heavy recoiling bolt actions. I also think that crimping is a good idea for ammo that absolutely must function, such as a once in a life time hunt or hunting dangerous game. For varmint shooting or target use, i do not use a crimp, in fact I avoid it when ever possible. I have converted several of my center fire bolt guns to single shots or load them one at a time.
I start out load development with jacked lead bullets about .020" off the lands. Once I find the best load for my particular rifle, I then experiment with the bullets at different distances from the lands to fine tune the load to find the best accuracy.
There are many things you can do to effect accuracy, but being as consistent as possible is probably the most effective way to influence accuracy. By consistent, I mean do it the same each and every time. If you are going to crimp, make sure each case is exactly the same length, so the crimp strength is the same each time. That is why I do not crimp, if I can help it, just one more thing not to worry about. Neck tension should be exactly the same for each case, so I load in lots and anneal necks when they start getting work hardened. Seat the primers the same each and every time. Seat bullets as straight as possible. These are just a few concerns of making a tight group...the list goes on and on I am talking just the loaded ammo, the rifleman needs to be as consistent as possible to make tiny groups. That is a whole 'nother story.
Bottom line... do not crimp unless you have to...You just have to find what works best in your rifle as far as bullet seating is concerned. I just want to add, that some rifles shoot best dirty and some like the bore to be squeaky clean and still other like it some where between.
Good Luck and Good Shooting
