There isn't any safety issue in sanding/filing down a burr here. A small fine tooth round file or some fairly fine sandpaper wrapped around a dowel/pencil/something
Sand it down a little. No big deal. Just make sure its smooth when your done. Or leave it and let the bolt buff it if it isn't breaking paintballs.
Dug this out today. I had a member ask me if I still had it in 2012.....I planned on lookin for it but I ended up forgetting about it. Never used