Give a rap with a hammer and point on the tube dovetail.
Just a little deformation to tighten things up.

 

Blue loctite

 

Easiest way is to use a center punch and raise a few dimples in the bottom of the dove tail cut.......NO glue NO hammering the barrel.......................BTW MARLIN deliberately left the front magazine dovetail cuts on the XLR"S loose so the magazine tube would not affect accuracy . My XLR is that way and when questioning Marlin. That's the answer I got.

 

Loose dovetailed mag usually enhances accuracy in a Marlin w/o the barrel bands. Just don't let the assembly get too loose.

 

A shim made from a beer or soda pop can will tighten up the dovetail with no hammering, dimpling, or permanent damage.

 

Used a shim made from a couple layers of aluminum foil. Tightened up just enough. Thanks guys!