Crono update...

Tried some Winchester factory 150gn Super-X - same velocity as the Federal factories: 2600 fps, but primers did not back out. Maybe the Federals were "undersized" headspace-wise. I've got some left over live rounds that I'll do the tape headspace check on (eventually).

My 144gn FMJ reloads did 2625 fps average, but with the added boom and flash. I originally had the crono about 2 m (6 ft) in front of the muzzle but it got knocked about a bit from the blast, and the first 2 readings were in the order of 6400 fps! I shifted it out to 3 m (9 ft) and it worked alright there.