I have a 300 win mag Browning A-bolt with a BOSS attachment. Browning beds the action of their BOSS rifles with a small dab of slightly rubbery material. I shoot a hand loaded cartridges of 165 gn SST bullets with 73 gn of 4831SC shooting at a velocity of 2947 fps (SD 23 fps). I didn't get very impressive results. I shot 5 groups of 3 rounds from a Caldwell lead sled rest. The vertical group size ranged from 0.5" to 2.2" at 100 yards. Due to the inconsistent grouping I decided to remove the Browning bedding material and properly bed the entire action. The rubbery material is supposed to dampen the harmonics and work in conjunction with the BOSS system. Hopefully the rifle improves instead of getting worse. I'll let you know how it goes in a week or so.