I finally finished the .20 Mrod project, and it's a tack driver! I bought a .177 Marauder and 2 extra magazines. At the same time, I ordered a .20 cal. barrel blank from Lothar Walther. The barrel took a LOT longer to arrive! After filling the .177 Mrod to 3000 psi, I fired 100 shots over the chronograph. I was impressed by the accuracy and efficiency. Then I tore it completely apart and measured everything so I would be able to machine the new parts. The rifle comes from the factory with 4 baffles in the barrel shroud but I decided to leave out 2 baffles in order to make the barrel longer, for more velocity. It's still surprisingly quiet. After machining the barrel, I made the new bolt and handle from a brass rod. The color makes it obvious that it's not a "stock" Marauder. The really challenging part was converting .177 cal. magazines into .20 cal. I had to make some fancy tooling to hold the parts for machining. I tuned the rifle for the Sheridan 14.3 gr. cylindrical pellet, because they have a better ballistic coefficient than regular diabolo pellets... and I have a bunch of them! I was hoping for 900 fps, but the pellets weren't as accurate at that velocity. After several hundred pellets across the chronograph at targets and lots of tuning, I settled on a combination that gives me 30 shots at 835 fps average, with a Standard Deviation of 7.07 fps, while putting all 30 shots into a dime size hole at 20 yards. Shot #1 starts at 2500 psi and shot #30 is at 2000 psi. So far it has taken 37 Starlings, 22 Sparrows, and 2 Ground Squirrels.