The is a very nice gun. Here is an idea you could consider, make all of your guns similar quality (to this one), make sure to save the blender file for each one, then work on making your game, you can then go back and edit the blender file later then update the model in roblox if you want to try to make it look even better later on!
I apologize if im a little late, but I think it looks great. I definitely think you should add more detail on the sides of the firearm and in the back of the weapon but I like it!