I took out my old MarkI lefty walnut TX200 yesterday. I think it is running at around 840 with 8.44 Exacts and I tried about 5 groups at 55 yards from the FT position. It was abit windy, but 1 groups was very nearly inside .5" edge to edge. I have this LGU piston that weighs 195 grams and a comp. tube that has had the o-ring groove machined off, to shorten the transfer port. The stroke is at 82mm. Has the LGU seal and the short transfer port to do away with most of the dead air space. I changed the piston and tube only and the shot cycle is sharper, but not really harsh. No chrono numbers, but I suspect it is spot on 800 fps. I tried a few sight in groups at 55 yards today and one group of 4 were all bunched in a triangular hole. Don't know where #5 went, but it was pretty windy. I'm going to give this one a go Saturday against some of the local FT boys. We are allowed a 3% cushion on the power level at our FT matches. I bet that would take some worry off all you U.K. shooters.