I have a couple of projects in the works using a Marauder/Challenger 2009 trigger in a Discovery action. The problem I had was that even though some have used this setup, I did not like the way the Mrod trigger housing with its 1.25" dia cut fit the 7/8" dia. Dicovery tube. I have a Challenger 2009 trigger on order, so I will see if it has the 7/8" dia cut which would go along with the tube used for the Challenger or if Crosman just uses the Mrod trigger and adds the funky bent metal trigger gaurd. This unit has the bent metal gaurd so I assume its a Challenger unit. Currently when tightened down, the housing only seats along the bottom of the radius against the tube. I wanted to create a better fit and prevent any side to side rocking so I thought I would cut the housing to 7/8" dia. At first thought that I would have someone do the machine work for me but I have been having a problem with the availability or willingnes of such people to do the work so I decided to tackle this myself.
I used a piece of 80 grit sandpaper wrapped around a piece of 7/8" dia tubing held in a vise. I worked the housing back and forth carefully keeping it straight cutting the majorty of the radius. Then I switched to 150 grit to clean up the cut and improve the dimension of the radius since this paper is thinner than the 80 grit. Then, as a final step, I used some rubbing compund directly on the aluminum tube to lap the final cut into the housing. It does not form a full 7/8" dia in the entire width of the housing but does create enough to seat it to my liking. I imagine I took off about .020" total at the crown.
My next thought was that the sear is now going to stick into the tube an extra .020" or so, so at the worst I'll take a bit off the top of the sear where the hammer engages it. I installed it onto a spare tube I have and put a hammer and pin in to test the seating and movement of the hammer. I quickly realized that I had more issues. The hammer was not seating itself on the sear, and the sear tab would not consistenly seat on the lower sear. I took the cover off of the trigger housing to see what was up. I found that the sear tab did not have enough clearance from the tube to let the hammer push it forward and seat on top of the lower sear. Instead it would bump into the front of it and as a result it would not catch. To remidy this, I took off about .020" from the entire length of the sear tab. Also, while pulling the hammer back it woud lock up before it made its way to the full rear position where the sear meets the front of hammer. This I noticed was caused by the very back of the sear arm catching on the back of the slot in the air tube. This area needs to allow the sear to rotate downward as the hammer pushes past it moving to the rear. To solve this I removed about 1/16" from the slot. Now the hammer moves freely back and forth into the cocked position consistently. Next I will cut a continuous slot in the bottom of the hammer to allow it to travel foward during firing and not bang around on the sear where the "half cocked" notch in the hammer is located. Also the sear will not drag on any portion of the hammer when the sear is tripped.
PS-I JUST NOTICED THAT MY PICS HAVE SOME SPELLING ERRORS, SORRY ABOUT THAT.