Monday, March 12, 2012

New Front Sight For The BSF S20

Still haven't started the rear sight project for the 22XX.  It's one of those projects that I have to be in the mood to tackle.  While I was thinking about it and the dovetail cutting it probably entails, I remembered that my BSF S20 WCM pistol needed a new front sight.

It's the weirdest looking thing.

I'd previously mentioned that the front sight wasn't appropriate for pistol shooting.  Really? "Barleycorn" sights on a pistol?  What were they thinking?

Removed the hood.

It's dovetailed in place.

Brass drift and a hammer blow knocked it out left to right.  Was hoping the dovetail was 60 degrees as I have a few dovetail cutters in that size... but it's not.  Didn't bother to figure out what it actually is--though it's probably 45 degrees.

Looks like it was made from a piece of round stock.  The widest dimension is approx.  0.500".

Cut a piece of "free machining" 12L14 steel. 

Faced the ends down on the lathe. 

This is a 3-sided 2nd cut file with a "safe" side--I sanded the teeth off one side on a belt sander.

Started to freehand cut a dovetail. Then I realized that I'd over cut the depth and had to start over.  Freehand cutting dovetails is insane asinine tedious.

Flipped the piece in the vise and cut the other side.  Just did it by eye checking against the cut in the barrel.

When it looked like it was close, I faced down the bottom of the dovetail in the lathe until it was almost bang on the money to the bottom of the slot width.

A couple file stokes here...

and there...

As well as some test fitting.

I quit with the filing when the angles matched and it would slide in about 3/4 of the way home.

Forgot to mention--the dovetail I filed had to be very slightly tapered so it wedges tightly into place as it's driven into the slot. The black mark is just a reference so I could shoot the pistol and verify its correct height to the rear sight.

Wanted the rear sight somewhere in the bottom third of it's adjustment range at approximately ten meters.

Faced the sight down until the height was correct and the pistol was grouping to point of aim along the horizontal plane.

Here's where it got tricky.  The dovetails are roughly parallel to reach other--not exactly parallel, but close.  I guestimated by splitting the difference in the taper and installed the piece in a 0.500" 5C collet.  (Actually, I just eyeballed it and thought it looked OK.)  The collet went into a holder called a collet block.  This is a square collet block and it allows one to rotate the piece in 90 degree increments. There are also collet blocks that are six-sided to allow for 60 degree work rotation.

Changed the set up and got rid of the parallels in the vise.  Located the block even with the end of the fixed vise jaw.  Set the travel on the mill and cut the flat that will become the sight blade.

Turned the block over and cut to the same depth.  Measured the thickness, did some math and set the depth gauge on the mill to produce a 4mm wide sight blade--my preferred width for shooting 10 meter pistol targets.

Turned the block upright and used a 60 degree dovetail cutter to undercut the rear of the sight.

Some clean up with a wire brush and here it is next to the original sight.  It's taller, as the rear sight used to be buried at the bottom of it's elevation adjustment.


A few milling marks on the side that aren't worth polishing out.  The close-up with the flash always makes the tool marks look worse than they really are.  Ya can't see them while sighting.

Tapped home.  Took a couple good whacks with a maple block to center the sight.  It'll never move again on it's own.  It's gotta be tight to stay put under recoil.

Those nice sharp edges that make sighting so much easier really chew up the hand when cocking the pistol.

Oddly enough, the hood fit exactly on the new blade.  Guess the old sight was made from a piece of 0.500 round stock after all.

It's perfect.  After a bit of shooting, I filed open the rear sight notch open to 3.8mm and the sight picture is ideal.

We'll have more soon.


Best Air Rifle said...

What lathe did you use? I'm looking for a small one for the shop.

derrick38 said...

I used a Taig. Blog co-author Nick sells them: