does anyone have a 3D model for the Doom 1 plasma gun? I'm planning on using a 3D printer but I don't have a model for it. If anyone can help that'd be awesome. scaling it to 2 feet 4 inches in length and 2 1/2 inches in width at the grip for practicality

The original plasma gun was a toy the ID team picked up at Toys R' Us. The Doom wiki entry for the Plasma Gun links to photos of one like it in the Notes section. With a little research, you might just be able to find the actual toy & use that. Good luck!

Jim has it right; to be more accurate, it was only half of the toy.

The entire toy is a small machine gun that is about as long as the Plasma Gun is in the game. However, it turns out that the front half of the gun could detach to be used separately; id took the detachable part (the bit on the right in the first photo that starts with block of black plastic) and turned it around.

If you are using that toy as a baseline for your 3D printed model, you'll want to scale the toy model up significantly; the base toy was small, but the detachable part is even smaller (you can see in that second photo how the user's hand almost engulfs it).

EDIT: I initially thought that the only part of the gun the detachable part was used to model was the barrel while firing; on closer examination, it turns out that the entire detachable does resemble the gun in profile.

I did a little more digging in the Doomworld forums; apparently the toy is a Rambo brand toy M60; variants show up on Google image, but damned if I can find one in the Google Shopping section. Maybe you'll have better luck, though.