
Anyway, since it wasn't obvious what was wrong with the BR chamber to cause it to hate gas checks, I elected to set the barrel back and rechamber. And as long as I was rechambering, why not try a 6PPC, since the BR had too much powder capacity for my cast loads? Well, because the Remmy has a 308 bolt head, that's why, and there are safety issues with some of the custom bolts that use an M16 or Sako extractor.
I considered converting a bolt to the Savage bolt head system. The Savage gas baffle would address the safety issues, and a PPC bolt head is available for the Savage. Only problem is the conversion costs money.

How to get PPC case capacity with a 308 bolt head? Well, I am not the first person to ask that question. Decades ago, match-grade PPC brass was scarce so benchrest shooters attempted to duplicate PPC ballistics by shortening a BR case. It was called the 6mm Talldog (sometimes spelled Taldog). It was a pain to make the Taldog cases so when PPC brass became readily available the Talldog was largely forgotten.
Nonetheless the Talldog would seem to meet my requirements, so let's give it a try. Here's the two cases for comparison. The unfired Talldog case has wrinkles at the neck from the forming operation -- I'm hoping the wrinkles will blow out when the case is fired, otherwise I will be forced to rethink my case-forming procedures.

No, the wrinkles did not blow out.


My TallDog chamber was cut with the same reamers as my previous BR chamber:
-- 0.270" neck (tapers to 0.269")
-- generous chamfer at entrance to throat
-- freebore starts out at 0.246" (the freebore has a slight taper)
-- 1.5 degree per side leade
-- the throat doesn't hit 0.242" until 0.200" past the case, so it's a fairly generous throat.
-- 1.415" max case length (0.140" shorter than the BR).
-- 26 3/8" barrel.
-- a fired case holds 33.5 gr. H2O, vs. 32 - 33 gr. for a PPC case (according to Quickload, anyway).