How big should a transfer port be...?

[Barryg]

The problem with the tx set up imo is the 2 o rings , and not so much the length ( long ports give soft cycle),I believe AA use 2 o rings to allow for more flexibility in the design to take up slack in the lock up , due to manufacturing tolerances, some lock up well some don't. The down side of this slack is the transfer port can hammer the end of the barrel, in severe cases it closes the lead in up slightly, which then sizes the pellet down ruining both accuracy and power.
When I make my own comp tubes I seal them in a completely different manner.

Correct me if I am misunderstanding what you are saying guns like the 77/97 and the Diana 460 are buffered by the front of the cylinder metal to metal with a small gap for the seal and T/P once the cylinder is fully forward, but the TX the seals are the buffer because there is a nut and not a flat surface like where the other two are buffered, you can see in the pics where the hinge pin bolt hole has made a mark on the 460 this couldn't happen with the TX nut.
I think that I disagree about the slack on the TX as I think the TX is supposed to have slack in that area otherwise it would put strain on the cocking link like it can on the 77/97 and crack if it's to tight, I don't really like the slack but these designs where before spring closing breeches

[NickG]

The slack doesn't protect, the lever,the clearance at the rear of the cocking shoe dies that .

[Barryg]

The slack doesn't protect, the lever,the clearance at the rear of the cocking shoe dies that .

But isn't it the clearance ( the loose shoe ) that causes most of the slack?

[NickG]

On the tx it's the position of the front face of the cocking shoe slot, It can be made so that there is no gap once the tube is up against the barrel (as it is once the piston is moving)the clearance is then behind the shoe. When you think about the breech set up as an o ring groove once the breech is closed it makes sense for there to be no gap.

[hmangphilly]

But isn't it the clearance ( the loose shoe ) that causes most of the slack?

Probably not an issue on many guns as friction from tight piston seal is usually enough to move the comp tube closed as soon as the piston starts moving .

[Barryg]

Probably not an issue on many guns as friction from tight piston seal is usually enough to move the comp tube closed as soon as the piston starts moving .

Yes that is my point except you don't need a tight seal lockup to start the process just a light pressure is best this is why there is slack in the TX setup to protect the seal and linkage as there is no need for a tight seal to start because it goes tight as soon as you pull the trigger on a sliding breech gun.

[NickG]

I know what you are saying, though I have found significant increases from having the port up flush with the barrel. The two o rings are a bad idea imo.

[hmangphilly]

I know what you are saying, though I have found significant increases from having the port up flush with the barrel. The two o rings are a bad idea imo.

Yeah .
But you're not running tight seals .

You renegade