Beautiful sunny day so I took my Marlin 30AS out to test the same load/bullet with and without gas check.
Win LRP, 18grains of H4198, RCBS 30-150fn at .310" from wheelweights queched in water.
I shot these targets side by side, one round gas checked, one round without and so on. Five rounds at each.
Factory open sights at 50 yards, six o'clock hold.
I had no idea the difference would be so dramatic!! I am now totally convinced that they work.
1Shot