I forget how to do it all right now, but being a scientist, I work in the metric system, so I used to remember how to convert everything in ft.lbs. I' d covert everything over, then change the mass, then covert it back, which takes a long time. If I remember correctly, if you divide your muzzle energy by your projectile weight in pounds, (you' ll get a huge number), then multiply this number by the weight of your gun, this should give you the ft.lbs. of energy transferred to you by your gun. (This is not always accurate because of stock design, anglular motion alters magnitude, inaccurate initail values, your gun doesn' t shoot the same as the test barrel, and about a million other sources of error). I didn' t check it out right now, but when I do it in my head, it' s coming out to be about right, since a .30-06 round in a standard rifle should have about 25-40ft.lbs at the shoulder. Basically, it' s like this, (weight rifle)(velocity of motion)=-(weight bullet)(velocity of motion)=(energy of motion), that doesn' t look right for some reason, but I' m certain in metric it is, there is a funny conversion factor from Kgm/s to ft.lbs. because lbs has an acceleration value incorporated.