Xausa--

Pardon me but I feel that Doubling doesn't have to give 4x the recoil as your calculations imply--

IMHO Your calculations would be absolutely correct if both barrels fired simultaneously, but if they fired sequentially the recoil should be less than 4x normal.How much less? Depends where and in what portion of the recoil curve of the first shot when the second barrel was shot.