TL;DR: Lapua averaged 45.815gr, Peterson averaged 45.615gr, with the Peterson being more consistently uniform.
Case capacities-
6.5 x 47 LAPUA -all fired in same rifle / chamber w/ same loads
LAPUA IS 3x Fired
Peterson is 4x Fired
Measured on 2 chargemaster Lights warm and calibrated
using 50/50 mix of water and 91%. Isopropyl alcohol.
Measured round robin style so I didn't know what case I was measuring.
The Lapua cases averaged 45.815gr with an SD of 0.07647gr
The Peterson cases averaged 45.615gr with an SD of 0.05871
This is right in line with my experience with Peterson VS Lapua. I have done these tests with 300 Win Mag, 260 Rem, 6.5 Creed and 308 and it's always between .2 and .3 gr smaller capacity for the Peterson. In my limited sample sizes it has also held true that the SD is smaller with the Peterson. Not by much, but they do seem to be more uniform. Hopefully this helps a little. Nothing crazy scientific but I'd like to contribute where I can!