404 Thats what I was thinking. When we were firing we just filled the mag which is only 3 and let them go. Then reloaded the mag for the next guy to shoot.
We did have some other rifles we were using to do load testing and just fired the 416ruger when we were waiting for the barrel to cool on the test rifles between groups.

I still think it has a bit to do with the dirty barrel but will wait till I get some more factory ammo to measure how much jump the bullet has before the lead