Dunno where you got the info that "the British" mostly used 26-inch barrels. The two original Rigby rifles in .275 had 23.5 inch barrels.
The last 7x57 I had built was with a Pacific Tool & Gauge reamer that had a "target" throat, shorter than most. I would tend to go with something like that.
To tell the truth, I'm using the 7mm-08 more and more these days. It gets the same ballistics with far less hassle, both in finding accurate loads and buying brass. I realize it doesn't have the "panache" of the 7x57, but am also tending to become more practical as I get older, having wrestled with lots of panache over the years. (That said, just spent yesterday morning at the range with an Marlin Model 1893 in .32-40....)
