How to change weapon animations?

Within Chris's .arc file you'll find a folder called motion which has his action.lmt, damage.lmt, etc. I'm not familiar with the SPAS weapon but if it functions like any other shotgun, you can copy the animation files and put them within that folder to force Chris models to always hold it like a particular weapon. There might be a better way to do it but I only know how to apply it to individual models. This means you'll have to apply them to every boy character individually since if I'm not mistaken, all men hold the Hydra like Chris.

If I recall correctly: Using the arc tool, extract the contents of a weapon arc such as the Striker (uWp17.arc). Find uwp17.arc, extract. Within the folders locate pl00wp17.lmt (pl00 means Chris, pl01 means Sheva, and generally Chris's base animation file applies to all men and Sheva's applies to all women). If you copy and paste this lmt into Chris's motion folder and rename it to uwp19.lmt and repack the arc and put it into the Archive folder replacing the original model, Chris will hold the Hydra like it's a Striker. It will also reload like the Striker too. To edit the individual aiming, you'll have to use the lmt tool to rearrange the animations. One thing to note is, when I mentioned all men share Chris's animations thats especially true in multiplayer mode. If you play Mercenaries as Chris with an edited weapon LMT, the game will only load 1player's setup for base animations. So if you both use the Hydra and yours is edited and the other man's model is NOT edited, the game will base the 2nd players animations off of Chris's. Thus both will hold the Hydra like your edited Chris. (Note that your friend, if they dont have the edited model, will see both hold it default).

Hope this helps. If its confusing, please feel free to DM me and I can share more it's COMPLICATED, but I've done it a few times lol!

Edit: It also occurred to me, maybe you can extract your new hydra file, and the striker (or other shotgun) and paste over the hydra's pl00wp19.lmt with a renamed Striker LMT, then repack and put into Archive folder. That might make it so all men now hold it and reload it like it's a Striker!