Sierra did a test not too long ago with the Lee Factory Crimp and without it. They found that some .223 bullets w/o the crimp were backset by as much as .2" in the chamber due to loading. This is from the "Experts" at Sierra. Take it for what its worth to you. Its a long article but well worth reading
http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm
Aim for the X
Stan
http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm
Aim for the X
Stan