Done both of my guns and it it super easy! Both transfer ports are drilled to .080" and that puts the Challanger rt to 12 FPE. However the bell curve will take it up to 14lbs without a regulator. I installed the Huma reg for the it and it is perfect, I have used it locally to win the WFTF Ft at our club..To bad there were only two of us shooting...lol
The only thing bad about the challenger is the stock. I made my own field target stock from a blank of curly maple and it was not too hard to do..
The Challanger is as accurate as my competition Steyr LG 110 rig. I even out shot the Steyer at my home course once..It is that accurate!
The 1720T pistol was given the same treatment of boring the port to .080" and then a Lane regulator. With some hammer adjustments I get 29 on point of aim shots before the Point of impact drops 1/4" for two shots then it drops offs qqqqquick after that. I adjusted the regulator to 140 bar to acheive this. The gun shoots the AA 8.44s at 780 FPS for 11.40 FPE.. If I use the 10.34 AAs, it gets729 FPS fpor 12.20 FPE
I removed the lawyer spring and readjusted the trigger. It is now breaking at 8.8oz. This will make the safety not work, so be careful.