Strange but true
i bought a absolute mint TX200SR .177 along with as new beech stock. When I chroned using various units I would get reading right on UK legal then the next near 13ft/lbs.
So yesterday I had in mind to check it it out and if need be get another Spring and bits baring in mind I have never took apart the SR before.
Gradually I get to the part of retracting the spring and looped around a coil was a O ring that was split and had attached to the coil. Cleaned every thing reassembled and on three different chronos I had 775-780 constant readings, well pleased. I'm thinking the O ring that was 10 mm dia and 2mm thick was acting as a extra power source. Where the O ring had come from I do not have a clue but if was left in a bag or something got into the works.