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. 

Wednesday, December 14, 2016

Mounting a Red Dot Sight on the Aeron B96 Part 2

Picking up from Part 1 

Finished the adapter by drilling and tapping two M4 x .7mm threads.

Gave it a coat of cold blue.  Normally, I'd polish out the machining tool marks, but it'll all be hidden by the scope base. 


Worked out the hole locations in the base to line up with the adapter and drilled away.

Flipped over, picked up the holes and counterbored.

Guess I took this pic before blueing the adapter.  Anyway, here's all the related components.

Ahhhhh, there's the blued adapter.   The adapter replaces the rear sight.


The scope base bolts to the adapter.


Blends in almost perfectly.

And, finally, the red dot is mounted nice and low to the bore axis.   A few sighting shots later, it was dialed in.  Should I ever need to add a picatinny rail to the pistol, it'll only take a few minutes to cut a piece to length and drill two holes.  And in even far less time, the iron sight can be refit and the pistol returned to original condition.

Monday, December 12, 2016

Mounting A Red Dot Sight on the Aeron B96 Part 1

Hey!  Back after a loooooooong hiatus.  Recently purchased a small red dot sight from Millett.  Thought its compact and lightweight size would make for a nice addition to a 10-meter style pistol.  The only hurdle?  Most 10-meter pistols have zero mounting provisions for anything save their iron sights.

I thought the five shot, semi-auto BRNO Aeron B96 would be an interesting pistol to adapt. It's a great trainer for rapid fire .22 pistol so the red dot would make it similar to the guns used for bullseye pistol matches.

Removed the two screws holding the rear sight.

They're M4 x .7mm thread.

The sight fits into a pocket in the frame.

Here's the Millett SP1 dot and a small selection of picatinny, Weaver, 11mm dovetail rails/mounts and assorted junk stuff on hand.   

The original sight has a width of 0.5515" at the forward end and 0.705" aft.  The pocket depth was about 0.230". After measuring all the various options on hand it became pretty clear that an adapter plate to fill the pocket would be necessary.  

This 1"/11mm UTG offset mount was also selected from the pile for my carnage.   Reasoned that it would be lighter than a separate rail and a set of rings.  Especially after I mill the dovetail clamp off.

Struggling to hold the mount, I used small insert vise to clamp the mount then clamped the insert vise into the milling vise.  Used a shop made fly cutter...

And shaved the mount down until it was completely flat.

Leaving this.

Checked the bottom to the lowest part of the radius at each end.  They're within half a thousandth of each other.  

A small piece of 12L14 free machining steel will be used to make the adapter.   I'll mill the thickness first.

Found some parallels.

They're used in vises to get short work above the tops of the vise jaws.

Here's the bar of steel  on the parallels clamped into the milling vise.

A few minutes later, the bar was 0.236"  Roughly 0.005"/0.006" taller than the pocket in the gun. 

Milled the 0.705" width down next.

I intentionally left the end hanging out of the vise to make it easy to measure as I worked it down.

Now we're here. 

The scope mount--I think it's now just a scope "base" will be bolted to the adapter, which will be bolted to the gun.

If you look at the pictures #3 and #4 above, the original sight is narrower in the front and wider in the rear--at the grip.  The front needs notched to fit.  A stop was clamped to the fixed jaw and the work butted against it.  The vise stop allows the work to be removed and relocated to the same place in the vise. 

Milled the first side.

Flipped the part over and cut the same depth/length on the second side, finishing at 0.550"-- a bit under the 0.5515" for some additional clearance.

Now I've got this cute little plate. 

That almost press fits into the gun's rear sight pocket.

Measured the hole locations from the gun and transferred that to the adapter.  Spotted, drilled, counterbored to recess the screw heads.

Uh, twice.

After I add a couple threaded holes to this plate, I can simply drill mounting holes into the scope base.  If that doesn't work out, I can drill a chunk of 11mm dovetail or picatinny rail.  With this adapter plate, the top of the gun becomes modular.

More in a couple days.