I'm having a difficult problem with textures for this model I made.

This is based on the original lasgun model, and I am trying to load the original texture onto it. As you can see, it fits perfectly on the modelling program, but when I try it in game all I see is the grey and white grid texture that appears when a texture fails to load. The only indication of a problem I see in the console is "trying Lgun.jpg..." I didn't change the .jpg used for the texture, nor did I change the .cfg or the grouping. Am I going to have to make my own texture(if so, I need help), or am I just going to have to make some changes with the files(maybe make it into a separate mod)? Similar issues with my attempts at modifying the look of the mass driver and Lucifer cannon shots.

this is what I have done on the MD, textures won't load on the scope or the laser(should I even include that?). As for the luci shots I made it shoot dretches and tyrants just for kicks, but the textures don't work there either(I think I have an idea though let me check it out).
One last thing, I am very new to modding and I spontaneously decided to make a mod that wouldn't change gameplay, just change some models a little. However, I can't really think of what else to do, so I want some opinions/ideas/preferences/tips/advice/etc. on what I should do. I'm still learning my program as I go, so bear with me.
P.S. Free cookies for anyone who can guess where I got my scopes from =D
*EDIT:BTW, if anyone can tell me where the client saves screenshots taken in-game, I would greatly appreciate it!
*EDIT:Nevermind, I found it. Screenies have been getting saved in some hidden folder that I couldn't see for some stupid reason...