Lots of ways.
- Damage to guns during recoil is effected at least to some extent to vibration during recoil. Simple measuring muzzle velocity is not going to determine how the load "shakes" the gun.
- muzzle velocity tells you nothing about how the load got to that velocity. I imagine that a load reaching its muzzle velocity rapidly will effect the gun differently than one that accelerates the load to muzzle velocity more smoothly.
- Think push vs hit - perhaps when it comes to felt recoil the microseconds difference is time to reach peak speed may not be noticable, but small canges in speeds of accelerations can have big changes on damage to mechanical things. (This in part is what is happening when you use rubber to dampen the blow of something. The total foot-pound force is not changed, but the time it takes to deliver that force is...)
- and on it goes. So much happens between the breech and the muzzle. If someone wishes to claim that only muzzle velocity (and ejecta mass) determine the effects of recoil I would think the burden of proof is on them. They would have to explain why a charge reaching (near) muzzle velocity in 6 inches affects the gun exactly the same as one reaching that velocity in 15 inches...
- Even chokes have a minor impact on muzzle velocity...
