Sounds like the probe seal is missing or split, or that the 'O' rings on the pistons are knackered, or - unlikely - something is blocking the transfer port. Generally a tough rifle. They are the most 'dead' shooting of the recoilless rifles, heavy but fascinating. That is a good price for a walnut one. Kev is a great chap, but it's probably a bit of a stretch to ask him for a picnic.