I’m have a 6BRA being built with a long throat. I intend to seat 105 Hybrids .075 off the lands. Mark Gordon of Short Action Customs has been compiling seating depth data on the 6BR, 6BRA, and 6 Dasher showing an extremely forgiving seating range between .070” and .085”. While there’s currently no dominant theory supporting Mark’s findings, a trend seems to be emerging in practice.
Although on an entirely different spectrum, whereas accuracy and expectations for consistent performance are concerned, factory “Match” loads for many of the newer standardized cartridges like the 6.5 Creedmoor and 6.5 PRC rely on lots of jump. Whether this is a coincidence, I can’t say.
In my case, I was quick to follow Mark’s lead after having seen similar results while developing 6.5 PRC and 6.5 CM loads for SAAMI spec chambers, both with the 147 ELDM and RL26. Last year, I started using ladder tests to identify seating depth nodes much in the same way they’re used to identify powder charge nodes. At extended ranges of 400+ yards (optimally closer to 1000), the vertical dispersion of impact groups on targets boards can identify seating depth nodes —if you’re lucky, really wide ones.
In the case of the 6.5 CM, I settled on .055”, but not really optimally. It probably would have responded even better to more jump, but I was up against case capacity. Reloder 26 charges became compressed and required vibrating or maybe a longer drop tube, neither of which were compatible with my criteria for a precision load expected to be produced by hand at a rate of 500 a month during match season.
To many, long throating a 6BRA to jump 105 Hybrids .075” will sound insane, we’ll see.
