Quote Originally Posted by ggggr View Post
Hi Mick---I meant making a full breech seal out of ptfe and then putting a hole in it, rather than actually trying to sleeve the transfer port itself. assumed that this would be ok as some people use ptfe to make breech seals for Cadets and Majors? Would hot air open up the hole in the middle if you more of less copied the Webley seal out of Ptfe but just put a smaller hole in it? The 4mm pipe would be handy for the centre of Webley pistol seals made of leather.
The trouble with the leaking hawks is that there are only about 2 threads on the plug, beyond the stock screw hole.At first I thought the stock screw hole was too deep but the air was actually coming around the thread. I think I used 271 loctite to sort it out.
Hi Guy

As Jim says the idea of reducing the transfer port is to raise the static compression ratio of the gun.

A standard MK2/3 Hawk has a swept volume of about 37 cc and the standard transfer port has a volume of about 0.201cc giving a compression ratio of 184/1.

If you sleeve the transfer port down to 2.5mm over its full length the transfer port volume reduces to 0.079 cc giving a compression ratio of 468/1.

2.5mm is the standard size of a Vulcan transfer port by the way --- so no flow problems with that size port.

If you just replaced the Transfer port seal with a PTFE seal/reducer I think there would be problems with the double reduction in transfer port diameter. The PTFE would probably erode as the air went through it and as Jim says PTFE has no memory so if you squash it it stays squashed.

I'm still experimenting with all this at the moment but I'm finding synthetic seals and O rings seem to like a compression ratio of in between 300/1 - 600/1 whereas leather seals prefer to run below 200/1.

This could explain why folks who change HW55s from a leather to synthetic piston seal don't like the firing cycle ?

On my favourite HW77 I have opened the transfer port up to reduce the compression ratio from its standard 1055/1 down to 490/1.







All the best Mick