So, I finally managed to get a little time to strip the Supersport today and have a look inside.

I already knew that it would need the cocking slide replacing, as you could see through the slot in the forend that the end of one of the side plates had broken off.

The rifle had been shooting very smoothly at 8.6ft.lbs with 14.5 grain Superdomes. Maybe a little more with other pellets? Cocking effort was very easy.

Once I had the stock off and peered through the cocking slot I was a little dismayed to see some of those dastardly square coils, announcing the presence of an OX / AirForce / whatever mainspring!

Hardly any preload made it very easy to release spring pressure....pulled the spring and guide out and the spring is broken and there are about 7 or 8 collapsed coils at the back end. Don't know if this is due down to a previous fettler collapsing them or fatigue. I didn't study it but just lobbed the offending item straight into the bin.

I couldn't get the sear to move out of the way to get the piston out, so removed the trigger and sear. This area was well gunged up anyway, warranting cleaning out. Apparently, much fun and games are to be had re-assembling the trigger? We'll see!

The piston seal looks absolutely fine. Not gone hard and no nicks or marks anywhere, so I'll re-use it.

The barrel detent spring is broken. Looking on Chambers, it says they're no longer available. Will see if I can obtain from Knibbs or Protek.

The main thing is that the cylinder and piston are perfectly fine, justifying continuing with the fettle.

Now, I worked on one of these many moons ago (1988) and really can't remember what the piston is like. I could just recollect those nasty rolled items in various other BSAs I had worked on years ago. Very well finished. And whoever has fettled it in the past has polished the rear bearing "bush".

Now, do I just get a standard mainspring? Does anyone have any recommendations? The end of the spring guide is a little rough and will have to be smoothed out. But, does the Tinny Bummed One make kits for these? Would a full Delrin item take the pounding reportedly sometimes dished out by these snarling little beasties? Should I use a weaker spring intended for a smaller model (like the Meteor), sleeve the piston but then maybe have to source a guide to fit? I'm thinking, maybe, run a standard spring and hope that the standard guide is a good fit, ask Tinners to do me a top hat and then, if there's the required clearance, fit a piston sleeve.

Oh yes, the washer section of the guide that acts as the spring bearing is a little gouged from the spring. So, if retaining that, I'll polish it out and then try and source another steel washer of the same size, so they can play happy spinning bearing games together.

Think that's about it for now. I just had time earlier to wipe some excess grease off most of the parts and all the little bits are sat in a bath of GT85 to de-gunk them.

Please feel free (especially anyone who has fettled these) to shout up with any observations / recommendations for springs / guides etc. And especially if you have a detent spring going spare!