Board Thread:General Nerf discussion/@comment-3362895-20200108112058/@comment-27306930-20200115174444

The internals of this thing look pretty straightforward. I think you're right, a thin layer of ABS epoxy or epoxy putty on the internal walls of the blue section of the breech in front of the feeder might do the trick. We're only talking about reducing 0.5 mm on each side of the barrel.

If you wanted to try a less permanent solution, you could try a couple layers of clear nail polish. It dries fast, builds up pretty well, it's tough, and if it's a total disaster you can simply remove it with some nail polish remover. Just a thought.