Slipping Scope Mounts on a Webley Patriot

Spring piston air rifles are notorious for their ability to move scope mounts rearward on their dovetail from recoil. The dovetail is typically 11mm wide and offers little surface area for ring clamping  To address the problem, many if not most such rifles come with a stop hole (or three) drilled into the top of the compression tube at the rear of the dovetail.  And most of today's scope mounts have a requisite recoil arrestor pin to fit into the hole.

But what if your rifle doesn't have a stop hole?  Or maybe it's not in a convenient location for your chosen scope mount?   Maybe your scope rings won't accommodate a stop pin?

Maybe this will help.


Backstory:  The cycling industry had a problem a few years ago when carbon fiber became common place.  The smooth surfaces and relative fragility of lightweight carbon parts presented a clamping and fixturing challenge. Carbon seatposts, stems and handlebars would often slip under rider weight.  Parts wouldn't stay in place.  Torquing the fasteners beyond spec was an all too common (and bad) solution as it deformed and crushed the carbon fiber ruining the expensive components.   The cycling industry's earliest and simplest fix was to have mechanics add a friction paste to the clamping surfaces of parts.  The paste contains fine silica that provides bite or "tooth" to the mating surfaces and substantially increases grip for the same amount of fastener clamping torque.  The cycling industry calls it "carbon assembly paste".  It's  available at any halfway decent bicycle shop or through the internets.

Finish Line Fiber Grip, Tacx Carbon Assembly Compound, Park SAC-2, FSA,  Whatever.  It's all silica in an inert carrier. 

OK, so there's all that.  What's that got to do with me?  I've got this hard kicking Hatsan Manufactured Webley Patriot.  It's a known scope mover and breaker.  I've heard of several now that have even broken the stock mounting bolt--including this one.  There's no conventional stop hole on this rifle.  Webley uses shallow cross grooves as the scope stop and that requires a special mount. 

I really don't want to try to find one--especially for a 30mm scope tube.  Just wanna use this cheap Walther red dot and mounts I already own.  Without a proper scope stop, figured I need to get as much grip on the dovetail as possible.  To increase my chance of success, I used an 11mm to picatinny adapter that has about 4" of clamping surface and four clamping screws.  The picatinny cross slots ensure the rings won't move.

Before installing the 11mm to picatinny adapter, I degreased, then gooped up the rifle's dovetail with Finish Line carbon assembly paste.  Tightened the bolts, then installed the rings and red dot. 

 

 

Gritty!

It's been a week and a hundred shots and it hasn't moved at all.   Obviously not a definitive test, but it's a good start.  This would probably also be the ticket on scoped IZH-61 rifles that have that plastic receiver and dovetail with no stop pin hole.  It promises extra grip without crushing that plastic rail.

Will this work?  It's definitely going in the right direction.  Without a mechanical stop, increasing the friction between the dovetails of the rifle and scope mount is the only other option to end recoil induced movement. 

I'm not exactly sure what constitutes success.  Guess it's going to be subjective.   For me, it'll be a success if the red dot stays zeroed for five hundred shots with no apparent shift.

Back to the Patriot

Got back to the Patriot the other day.  Wanted to reduce the airflow through the transfer port to create a slightly larger cushion of air in front of the piston.  The hope was that the "ping" from the piston hitting the front of the compression tube would go away.  Tore the gun down again and jumped in.













Didn't bother to go through pin gages to find the actual size, but a #20 drill bit (0.161") just fits.
So, the transfer port is huge--about 0.035" larger than "normal".  There are a lot of ways to reduce the port size.  Could've drilled it out even larger, threaded the hole and made up several set screws with various sizes of through holes.  Or made interchangeable sleeves that are secured with a perpendicular setscrew.  Could've done a bunch of work, but the gun's firing cycle was so harsh, and with the end result unknown, I couldn't find the motivation to spend the hours doing the machining.  The fastest, easiest way to see if this idea would work would be a simple reducing sleeve bonded into place.  I've done this very same fix in the past on a Haenel 303-Super.

Turned a piece of brass to 0.160" then drilled a 0.135" hole down the center.

Leaving a very thin walled sleeve.

Mixed up some quick setting JB epoxy...

and pressed the sleeve in just below flush.

I know.  Not much to it.

No protrusion to catch on the edge of the base block.

While it was apart, I removed the main pivot's locking bolt. 

And found a replacement socket head cap screw.  Just taking it to length.

Also reduced the head's diameter by a couple thou.  Here it is re-blued.

And installed.  Well, the pivot bolt looks a bit ragged.  Might need to turn a new one at some point.

The sleeve is a success!  The noise is gone and the rifle is producing just over 28 foot pounds with H&N Baracuda Hunter X-Treme pellets(670 fps).   H&N wadcutters are moving out at 740 fps. We'll call this a victory for the moment.  The gun still has a pile of recoil no doubt due to the sheer weight of the huge mainspring and the heavy walled piston.  Reducing the piston weight may just be on the list. 

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.






























Spotted.



























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.

Webley / Hatsan Patriot Tear Down

Picking up where I left off.  Removed the stock from the Patriot and set it aside once again.

A few pics of the trigger components from various angles.  (Just in case I need them)

Wish all the pins had retaining clips.








Three pins secure the end cap into the compression tube.  The front two also hold the trigger housing.  Removed the forward-most pin.







Then the middle pin.  With this middle pin out, only the rear pin holds the the mainspring from firing the end cap into the wall.  Or your skull.  Take heed.

There's another pin to remove before the trigger unit will detach from the compression tube. 

This pin is both a pivot for the upper sear as well as a slide for the trigger block safety.

Trigger unit pulls straight down and it's out.






I realigned the pivot hole in the sear and slipped a drift into place to act as a slave pin.

Another view.

I wouldn't consider taking this gun apart without a mainspring compressor.  There are already picture online of injuries sustained from attempting such.    With the gun secured in the compressor, I knocked out the last pin and backed out the end cap.  Expect to need about 4" of travel in the spring compressor.

Some type of glass-reinforced synthetic. 

Sliding safety is reminiscent of the Feinwerkbau 124/127 series.

Under the lever is a plastic detent ball and small spring.

After the end cap, the main spring pulls out.

The spring is huge.  At 14.5 inches, It's--by far--the largest spring I've ever encountered in an air rifle.  The plastic spring guide looks like it's made from the same material as the end cap.

Removed the barrel pivot locking screw next.

And the pivot bolt.  The barrel assembly now just pulls out of the forks and the cocking lever pops out of the piston.

A nice surprise to find shim washers on the breech block.

Like the mainspring, the piston is also massive.

The seal looks burned.  The lip feels hard and not at all pliable. 

I think this was the main culprit in the harsh firing cycle.

Inside the piston body, there was another piece of synthetic that the end of the mainspring seated against.  Seems to have acted as a rotation washer of sorts.






The heaviest walled piston in the world? 

Ordered up a new piston seal from Jim Maccari at Air Rifle Headquarters.  Should have it in another day or two.  The plan is to replace the piston seal and add some buttons to the rear of the piston skirt.  Also considering a longer, tighter fitting spring guide and perhaps a short front guide, too.  We'll see what shakes out.

More soon.