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The jbm calculator is using an exit velocity of 4700ft/sec to calculate the contribution of the propellant.
I believe this was also the figure given historically in Sierra handbooks.

I'm not singling you out. I'm referring to comments like the above that are incorrect, because clearly it is the velocity of the projectile/s that are being referred to.

I disagree. Basic understanding on recoil necessarily begins with balancing momentum.
The article the OP linked to contained all that was needed for him to answer his own question without being...

I doubt it. Turning in his grave more likely. Recoil calculations are based on conservation of momentum.