Originally Posted by Tench
AA in their wisdom (?) don't use a gland seal on the firing valve stem, this causes air to leak down the valve stem when the transfer port is under pressure during the firing cycle. I think this hole also allows air to escape during the forward travel of the hammer. If this is the case blocking the hole will slow the hammer and reduce the power. Blocking the hole will also cause the air escaping down the valve stem to blow the hammer back causing a double (or more) tap on the valve, this is most likely what people hear when they say the sound of the gun changes. Basically it all comes down to a design that cuts corners, unfortunately loads of different makes of rifles are made without stem seals.
With the exception of BSA I cant think of another maker that uses valve stem seals on all their designs?
Thanks Si , I thought there was more to it than just the hammer pushing the air, I did check 20 pages of your posts before pm ing you
FTP900 MTC connect,Welhamanium internals -sorted
HFT500, ACZ stock MTC connect
TX200 Mk3 CS1000 stock, hawke vantage sf , Nick G internals
Steyr ?, maybe , they cant all be wrong?