After many attempts tuning my 30 year old leather piston washered HW35 using the excellent advice contained on this forum, I have happily been running it for the umpteenth time - the latest reason being the replacement of a snapped mainspring.

This item was one supplied in a tuning kit in the 80's along with Cardew's tuning book yet being honest the gun has never lived up to expectations. The new spring is a standard secondhand Weihrauch item kindly donated by Airgun God. In addition I have now radiused/deburred the transfer port and fitted a plastic sleeve to the inside of the piston together with Delrin Top Hat and Guides supplied by chambers.

The rifle is shooting very sweetly: The horrific twang and erratic grouping have been replaced with a very good grouping but it seems the rifle is well down on power despite having around 2-300 pellets through it since the last rebuild and approximately 1600 shots since the Piston/cylinder/washer etc were tuned.

The leather piston washer was sized so that the piston just falls under its own weight unless the transfer port is blocked.

I don't have a chronograph and the power has only been compared to a 30 year old Mercury also in .22. The comparison is very unscientific: Using a variety of pellets at 10 metres into a steel pellet catcher, the pellets from the Mercury are always significantly more flattened than those from the HW35.

The Mercury is completely untouched and I am forced to conclude that the HW35 is producing a lot less than 10ftlbs.

Where do I go from here please?