For the M40A1.....This info was given to another shooter from Gary Schneider of Schneider barrels:
The M40A1 barrel dimensions were 1.10-1.210 +/- X4", straight tapering to .890-.910 +/- @ 26.5".
After cutting and threading the breach end you would end up with 1.20" X3", +/-.
Once it was threaded at the breech end they(the USMC armorers I believe) would trim the muzzle of the barrel to 24" from the front of the trued recoil lug, as is their method of measurement, making the muzzle approximately .920-.940, again +/- .
He stated there were variations of +/-.015", maybe more at times.