[TomTom]

To close the discussion, stealing from Bobot 4.06d, you need to copy 26 files not counting limbo menu ones. Two files have to be renamed and their animations reduced (say \weapons\shotgun_axis.weapon -> \weapons\kar98.weap and say \weapons\shotgun.weapon -> \weapons\m1_garand.weap and comment out the part 6 and part 7 blocks inside these files). And one file can optionally be edited to make rifle reload animations longer. Unfortunately the proper shotgun reload animations need code changes (possibly client only changes would work but then what would the other players see you doing?). The limbo menu weapon graphics are massed into a couple of files so that would take a game graphics editor to change them.

So what will you get?

A shotgun model in your HUD (one handed, cause we commented out the arm in part 7 of the model), and an icon. A proper dropped weapon model in the game, and mostly proper weapon in the hands of your engrs (when they chose to use a rifle not a rifle-grenade). And sounds near and far of shotguns.

what feels wrong?

Proper reloading, the allied shotgun only reloads when empty and then 8 shells in one go (and an invisible hand doing it). For the axis they can reload at any time but again to the 10 shell maximum in one single motion. Both guns fire a bit too fast, too accurate, too far, too narrow a spread. And the model changes instantly back to a rifle when you do a weapon switch to load a rifle grenade (note to clarify, snipers don't get the shotgun).

BTW the rifles are the best fit I could find for substitution given operation and number of parts to their model (though the silenced pistols are close too).