I just see how to get away from the wall color. You're limited with what your background color is going to be. And if you edit the image onto some other background, you really wouldn't be able to tell whether the image was shot vertically or horiztonally.
I even thought about going to Lowe's or Home Depot and buying a 12" square tile and using it for a background. Something like slate or marble or quartz. Just something different.
If I put the grips on the gun then it might be easier to get the gun to stand up so I could shoot horizontally. But I have a shiny silver gun and most people have black ones. So I think it will keep people from seeing the possibilities. Kind of like if you sold wheels for cars and your pictures were always of the same color vehicle, people with different color vehicles may have a hard time imagining what it would look like on theirs.