I have recently scrounged a Bsa Cadet action off here and a stock as well from someone else. The piston is with my neighbour to weld up a bit of wear just behind the cocking slot. I've made a piston washer ready for when it comes back and fitted a DCL Dave breech seal in the barrel. I cleaned the bits up and decided to "borrow" a piston out of another gun today. I cut 2 brass 1BA screws to size for the front stock scews (should be 7/32 BSF-----but 1BA is very close and should be ok with them being brass) and found a 2BA for the rear stock screw. I put the action together with the spring that came with it as I cannot find a Cadet one here. I tried a couple of shots from just the action and it barely shifted a pellet. I decided to try blowing down the barrel to see if the breech seal was leaking. A lot of air could be heard. I then put my fingers over the stock screw holes and the air leak stopped! It is actually leaking from the left stock screw. I don't think someone has forced a screw in and I don't think it is leaking from round the thread, like a Webley Hawk I did years ago. I think the thread has gone too deep and maybe just touched the transfer port wall. You cannot see anything by shining a torch down the cylinder and poking something into the screw hole.
The good thing is it does not seem to leak when the stock screw is in. I may end up putting some gunge in the bottom of the hole-------or try a bit of tube in the transfer port to see if that stops some leakage-----just out of curiousity.

When I got the action in the stock, it didn't want to cock, partly as the trigger was catching on the guard and partly due to rubbing on the slot in the stock. A few touches with a file seems to have sorted it out. I'll attempt a plink if the weather is ok and await the return of the piston so I can refit it.