I don't believe a TP smaller than 3.0mm ever works in a 12FP springer....

[TonyL]

I was thinking about making a brass insert as a transfer port, my idea is to make it tapered down from compression tube, with a convex entry, so no sharp corners, highly polished [mirror]. My theory is based on - as a youth I used to polish cylinder head ports on my motor bikes & it did improve performance - better intake/exhaust flow. just an idea at the moment?

There has been a number of findings from experiments conducted shared with us over the years and, if I remember correctly, the short answer usually boils down to no fancy shapes / bell mouths etc required. Just a nice, parallel, smooth port with no sharp, jagged edges. I think one of the links that T20 posted onto the thread about HW80 transfer port size to the Pyramydairblog shows a few experiments with differing layouts and I'm sure I've seen plenty of others in the past. That old thread is now on page 1, by the way.. Jim has provided some brilliant information over the years on the subject in Airgun World.

As has been said up above, all very interesting and intriguing stuff.

[cringe]

There has been a number of findings from experiments conducted shared with us over the years and, if I remember correctly, the short answer usually boils down to no fancy shapes / bell mouths etc required. Just a nice, parallel, smooth port with no sharp, jagged edges. I think one of the links that T20 posted onto the thread about HW80 transfer port size to the Pyramydairblog shows a few experiments with differing layouts and I'm sure I've seen plenty of others in the past. That old thread is now on page 1, by the way.. Jim has provided some brilliant information over the years on the subject in Airgun World.

As has been said up above, all very interesting and intriguing stuff.

OK, thank's for that. so it's back to the drawing board for me!