When I started BR we only had the Sako 220 brass. When Laupa made their brass it changed lot of things
Here is real reason BR FL size
Custom Dies Work Best
Most top 6PPC competitors run their ammo at pretty high pressures. Such pressures demand that cases be full-length sized each time they are loaded. But the trick is sizing the case just enough to allow proper feeding/extraction and no more. To achieve this perfect fit, nearly all the "top guns" use custom dies, precisely fitted to the dimensions of fired brass. Typically, a custom sizing die will reduce the case diameter at the shoulder .00075" to .001". The die will also allow for a little bit of shoulder bump. Nearly all the top shooters use bushings for neck-sizing. Having a variety of bushing allows you to compensate for brass that becomes work-hardened. You can also use bushings to tune loads for different bullets or conditions (tighter "grip" tends to increase pressure). For his .263"-necked brass, Speedy Gonzalez has a full set of carbide neck bushings, in .0005" increments from .256" to .261". He also has four different body-sizing dies, which allow him to choose the exact amount of sizing he wants, both at the shoulder and at the web.
I should add other improvement was Redding Small Base type S sizer for the 6ppc as some made reamer for that die.
http://benchrest.com/showthread.php?...e-die-question