For those of you that are wanting to run different barrels in your MR5, Jim Lange started making MR5 compatible barrel adapters.
Here are the pictures of the adapter, they cost $50 and can be obtained here
. I haven't fired through it yet, gotta find some air first.
I thought it looked familiar, after talking to Jim he confirmed that he made the MR5 adapter from stock barrels. Quality is top notch.
Testing with J&J barrel
Shroud fits fine over J&J, I also got an empire barrel system, shroud doesn't like that one sadly.