I put gas checks hornady and got good grouping.
One of my boolits had a check gas done with a check maker and the POI was markedly higher. The boolit is 314299 50% soww and 50% linotype, PC and lubricated with simple lube.
It was a single shot so I can not generalize. I use a load of 28 grains of Argentine powder that is similar to 3031. I do not measure it but it must be around 1900 FPS
I'm going to need more tests