Wednesday, July 25, 2018

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. 




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.