So I shot the 7mm WBY 150gr load and it was a bit faster than expected as it was 0.5gr under max. Then I shoot the 300 WBY 150gr load that is at max and it was at the same speed, using 20gr more powder. Stupid chrony. Back to the bench...

Sometimes muzzle blast will effect the readings. Back off another 10 feet and look for a change.
Good luck!

My chrony just reads the last # if you are too close and it picks up the blast. I had that with my 338Rum and a 378 in the past and had to move back. Some guns move the chrony if you don't anchor it too! Lots of fun over the years but havent shot one yet!!!!

I had to set mine back like 15 feet when shooting my 257 wby. I blew the screens off the chrony. I thought I had hit it, but no, just "blasted" them off.

It was definitely an "uh-oh" moment there.

PoppaW,
Maybe the 300 bee doesn't like the barnes bullets as much as the 7mm. Maybe try a different bullet hmmmm.......let's say possible NOSLER.