Quote Originally Posted by AC all day View Post
Spot on exactly....it is a slip on silencer.
I have given it a gentle tap and yes it does hold the underlever but iirc from previous 77s you should just return the U/L and it snuck into place....there is slight springiness in this.
Currently there is no breech seal or mainspring in this and it's springy. As said before the crown of the compression tube is slightly raised by a mm or 1.5....
I have also just looked and 25mm tubes are rare so will 26mm fit??
A 26mm cylinder/piston assembly will fit.

I'd try putting a pellet in the barrel but leaving it's tail hanging out then closing the lever --- if the pellet is pushed fully into the barrel it tells you if the transfer port is hitting the barrel.

If the pellet remains proud of the barrel then the crown could be the problem --- easiest solution is to machine the crown on the cylinder back.