You could certainly get a custom tap.
I did, and the thing on the end of the barrel looks like it was made by the team of Fred Flintstone and Homer Simpson.
If I had not hit my house with a tree in 2014, I would have completed that Mosin Nagant rifle and hunted with it in 2014. I have designed pillars for it and bedded them with pre compression. The front pillar looks like a toilet.
It should make a great hunting rifle in 2015.