well the model is just translated back along local z, which is possible because its a separate model and not a submodel. thing is the whole gun would need to recoil, and you might need to add yet another model for the gun mount since you cant translate submodels the way they can be rotated like with gatling guns. you can also completely do away with the mount and just model that into the ship and only model the recoiling part (which is acceptable for me at least because i've been modeling the mounts as part of the ship). if you wanted to have a non-recoiling part like a recoil slide like on a howitzer, and wanted it to be interchangeable (not part of the ship) that would need to be another weapon model. despite the caveats it still it seems possible, you just have another model to deal with.