Your equations are applying conservation of momentum to the system (and getting the same results I posted above), not conservation of center of mass.Put your junior high school math cap on if you want the equation.
300 PRC
Bullet 200 gr x 22” length of travel in barrel = 4400
90 gr of powder that has moved it’s center of mass 1/2 the 24” barrel length = 1080
Those together have to equal 8-1/2 lb (59,500 gr) x distance rifle moves.
(4400 +1080)/59,500 = .092”
6.5 creedmoor
(140 x 22.5 + 44 x 12)/59,500 = .062”
223
(77 x 22.5 + 25 x 12)/59,500 = .034”
When I remember something wrong I don’t have any problem admitting it - the distance is much less than 1/4” - the Creedmoor is right at 1/16”, the 300 PRC is 3/32” and the 223 is about 1/32”. Old age is a bitch. Lol
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