Pretty hard shadow right behind the gun there. The hard part of shooting markers is standing the gun up so that doesn't happen.
I've been using some clear plastic pillars to prop guns up. I think they were meant for wedding cakes or something. Since they're transparent, they'll largely disappear in the blown out white background. Sometimes a few edges remain, but they're trivial to remove with dodging or erasing.
Here's an example. Without any editing, the shot looks like this (Note I've also got edges and dust to remove here):
You can almost see the pillar there. Here it is with the curves pulled way down:
The finished shot, after cleanup and processing: