Will....not real sure either.Could be the transfer port....which would be the only plastic part. Anyway...getting all ticky about it..while we call that the transfer port, it's not. The holes in metal leading from the valve stem to the barrel would be the port (or ports)....the plastic part on the QB would be more like a port gasket as there is no metal part between the tube and the breech.If that's it...it's at least use to be a somewhat "squishy" rubbery type, that would read bigger on hole dimeter outside the rifle, but would often close up when the breech was tightened down. Most folks just made one from ice-maker tube, but there were/are lots of more complicated or creative ways.
The material the factory used was soft enough that it squished a bit when the rifle was assembled. So while the hole measured one size out of the rifle, it was actually smaller once squished together. Doesn’t help that there really isn’t a good seat on the bottom of the receiver.Usually it ended up being the smallest hole from the valve to the barrel, so we just make a new one with a bigger hole.Lot of us just used icemaker tubing….but the trick is getting it just high enough to seal, but not so high it buckled, Certainly works once you get just the right fit…. also demonstrates whey the factory used a soft/squishy “fit everything” version to crank them out. Also expalins why so many QB shooters report way different pout the box speeds (some just squish more than others).Actually….most icemakers have enough slack in the connecting line that you could disconnect and cut off more than enough for making dozens of them.-------OK...pulled some parts out of the parts box.Hole in the valve runs a pretty generous .185”Hole in a .177 barrel runs about .125”If the transfer port (gasket) passage is less than .125”...you’d gain speed over factory size by making it .125”. If it’s not a squishy material, likely it would stay whatever size you made it once reassembled.If you made the transfer port (gasket) larger than .125”, would still run into that sized restriction just above it.Making the transfer port (gasket) hole larger that the .125” restriction just above it wouldn’t hurt anything, but wouldn’t gain much either.NOT talking about all the ways to make for even better gas flow….just the simplest way to make the existing system work to it’s base-potential. Past the transfer port, are gas flow mods that you can’t easily reverse.
Icemaker tubing (0.250” OD, 0.170” ID) is a loose fit…the recess is closer to 0.275” (7mm). The tubing is a time-tested solution and so is the Crosman transfer port seal. The OEM seal has a very restrictive ID by comparison.
This is a little off topic but bear with me a moment, I bought a 177 barrel and bolt from Archer to replace the 22 barrel, it eats up bolt seals like crazy even though I've polished everything. Archer charges way to much for them, does anyone know where they can be bought in bulk?