Transfer port size

[Shed tuner]

If it slams close it, if it bounces, open it - but best to leave as is and fine tune the piston weight instead - it a combustion chamber, not just a port

[shrendi]

I have without any problems taken the 77 port out to 3.3mm.

[baz]

I have found that tapering the port and putting a slight radius on the piston side of port works, if in doubt leave well alone

Baz

[Ray J]

I read somewhere that the port on a springer is designed to give a miniscule Dieseling effect. Therefore, is very precise in its specification to the rifle.

Try a search, it has been discussed before.

Ray

[shrendi]

I believe the timing of the shot is a combination of pellet fit and wieght, swept volume, spring force, piston momentum and port size. You need peak pressure to be reached before the pellet starts to move and then to fall as rapidly as possible without piston slam. Any change to these variables yeilds a different shot character. If you increase the port to much the peak pressure will never be reached, to small and it will not be released over a short enough time.