Sunday, March 30, 2014

Webley Hatsan Patriot Piston Buttoning and Spring Guide

Still working on the Patriot.  Here are a few additional pics of the damaged piston seal.

The face of the seal has actually melted from the adiabatic heating of the piston's compression stroke.

The Maccari replacement seal.   While this seal is listed as fitting the Hatsan 135, it's also correct for the Hatsan manufactured Webley Patriot.

Gonna button the rear of the piston.


Drilled three 5/32" holes around the circumference.

Turned down some acetal.

Left the pieces about .002" oversize in diameter. 

A drop of superglue in each hole and then each button was pressed in using a vise.  Overkill, as the press-fit alone was probably more than enough to ensure that they never come out.

The buttons are far too long and can be filed, sanded, carved down to size.

--Or turned down in a lathe.

They're about right when it takes some pressure to seat the piston into the rifle's compression tube.  The "buttons" act as stand-offs, preventing metal-to-metal contact between the rear of the piston and the ID of the compression tube during the firing cycle.  The front end of the piston is held away from the tube by the piston seal.

Now for that longer spring guide.  The stock spring guide is in the center.  Was gonna make a new one from scratch out of acetal, but I found a couple old mountain bike suspension fork spring guides from Rock Shox.  The shock forks are long gone, so this is a good time to re-purpose.   The grey rod on the bottom is about the right length.

First, I drilled a counterbore in the base to fit over the boss on the rifle's end cap.

Rounded the end, then shaved the diameter down until it just barely fit into the spring.

Transferred over the nylon and steel washers.

Thin coat of moly grease on the sides of the piston seal.  The moly on the piston body is really just there to prevent corrosion.

Piston in gun followed by the Spring and guide.  Rifle went back together in the reverse of disassembly.

Almost forgot.  Didn't like the thick, painted finish on the safety.  Finish was removed by media blasting then the metal was darkened with Birchwood Casey Aluminum Black.

Good news:  The Patriot is putting out 733 fps with H&N .25 cal wadcutters and the firing vibration is gone.

The bad news:  There's a very slight metal "ping" at the end of the shot cycle which I attribute to the front of the piston kissing the face of the compression tube.

This is becoming a semi-trend lately and if you're a regular reader (thank you), you can probably already guess as to the cause(s).  The transfer port on the gun is pretty large.  The bore is also on the loose side.  I can fix the transfer port, so that's up next.