Are we talking a hang form an AR 37mm or a break action single shot 37mm? No experience with the hang form an AR kind but my department tested 37mm break actions vs. 40mm break actions for less lethal use in our jail and I was very surprised to find out the 37mm recoil was much more stout than the 40mm. The sales rep said it had to do with case length. Something about the 37 mm cases being considerably longer than the 40 cases to make up for the lost width. Basically the ammo designers overcompensated and the 37's are brutal to shoot from the shoulder, similar to a 10 gauge 3.5 magnum slug from a 20" barrel. The 40's are easy though, similar to high brass 12 gauge bird shot.