As the title implies, I’ve had to find yet another M4A1 model. I had recently recompiled the previous one incorrectly (the game started running at ~20 fps), and I didn’t have the original Blender file with correct normals. The new model (link here) was created by Twinke Masta of FPSBanana. Screenshots of it in-game can be found here.
Edit: I realized it ran at 20 fps because of a program I had running in the background. However, I would have to re-export the model anyway to add moving parts (like the bolt release).