Expense, I purchased a 30/06 seater die, an 8mm bullet guide and an extended shell holder for 308 W, with the added parts with the seater die I can seat 30/06, 8X57, 8/06 and 308 Winchester. There are two seater dies offered by RCBS, one (black oxide) with a rubber 'O' ring for resistance, the other has a detente adjustment, one can be used with a progressive press and is offered with different bullet diameter guides, the case neck is centered, the bullet is centered, when seating, there is no mystery as with standard seater dies, place a bullet on the top of a case for the ride up to the top, unsupported, for seating, it is done all the time with success, I like boat tail bullets for that reason. I have a universal 7MM by Lyman that allows loading bullets through the side for alignment, except for the extreme length from short to long cases it works for 7MM.
Weatherby made Universal seating dies with caliber specific guides, I have one in 257 Weatherby, chrome plated, once the case raises the guide and bullet the bullet is held between two centers, If the hand loader does their part installing the case in the shell holder the bullet seats with precision, worth it? not for everyone and not for every cartridge, there are differences between the 3, RCBS, Lyman and Weatherby, The RCBS and Redding offer more neck support.
F. Guffey