People love to criticize without helping, that's apparent in almost every thread. OP, you should just expect it.
Anyways I'll give you a few pointers.
#1 Jpg is NOT used for 3D meshes period, idc if it is your first model or your last, it is a bad choice. A better choice would be DDS since it is loaded directly by the video card rather then being uncompressed by the CPU, loaded into the ram, then loaded into the GPU.
#2 Using a render or a picture as a texture is not a good idea. Although it is done fairly often in this section (/facepalm) it would be frowned upon anywhere else you would go.
#3
Topology is very important in the rendering of meshes. To give you an example of how topology effects the efficiency of graphical rendering think of a deck of cards, it is easier to pick up a flat row rather then 52 individual cards laying on the ground. An example of correct shotgun topology can seen
here. Just work a little harder on vertex loops rather then getting the least amount of vertices possible.
#4 Remember to rename your mesh INSIDE the elu as well as the actual elu name. At the moment yours is named Cube.002, rename it desert_shotgun or something of the like. Also remember to keep spaces out of names, always use underscores or leave them out entirely (this also needs to be remembered when making the elu name, eg Desert_Shotgun.elu).
=o