Sunday, December 25, 2016

Aperture for the Crosman 118

Been shooting my late grandfather's 1954 Crosman 118 and wanted a better sight picture on paper targets.  What the heck is a Crosman 118?  It's a bulk-fill CO2 gun with a 10-shot bolt action mechanism.  Think "Benjamin Marauder from the mid 1950's" and you've got the right mental picture.  I've seen aperture sights on this model before but this one has a simple V-shaped sight.  From the looks of the top cover, its drilled to mount a sight in two different positions.  I think the rearmost holes are for the aperture, so it was probably an option. 


Top cover and sight.

The V shaped notch sure didn't do much for paper target accuracy.  The stamped sheet metal sight is about as simple as it gets so I don't want the replacement to stray too far from that.

Had some spare sight odds and ends in the parts box, and found this unused Crosman 411 aperture from a previous blog project.

The sole complication is the (now) unusual #12-28 thread pitch.  I didn't have a tap in the correct size, but I did find a few in the massive tap collection drawers at work.  With the boss's approval, I borrowed one for a couple days.

Gonna make the sight base from a scrap of steel pallet strapping I pulled from the trash at work. It's springy stuff.  Need a spacer and a nut, too.  An M5 x 0.8mm will be easily rethreaded to #12-28.  This is about the laziest easiest way to make this project happen.

Drilled out the spacer.

Faced down the end.

Used the Taig lathe to get the threads cut square.

Spotted the mounting holes by using the old sight.  Easy.

A center drill was used to make the holes.

Filed the overlapping holes into a slot for windage adjustment

A little shaping on the bench grinder.  Hey, just because its a piece of steel strapping doesn't mean it has to look like a piece of steel strapping.

And into the vise for a 90 degree bend.

Installed on the top cover.

And I hate it.  Its perfectly functional, but what was I thinking using a machine nut? 

Scrounged up a knurled sling stud mounting nut with a #10-32 thread and re-tapped it to #12-28.

Looks like it's been there all along.  It pivots for windage and the elevation is taken care of by bending the sight base vertically.   In practice this actually worked just fine.  It was on target in four or five shots and has a noticeably cleaner sight picture.