Sunday, March 6, 2011

Installing the T/C Sight and Making a Front Sight Adapter

With the T/C sight essentially finished, it was now just a matter of finishing the installation.

Removed the steel breech from my 1750 pistol project.

The curvature of the base of the sight just covers the dovetail in the Crosman breech.

Removed the elevation screw from the sight.

And pivoted the sight forward. Forgot to show the spring. Note the two mounting holes in the sight base.

The sight is hinged at the front with a small roll pin. I'm not going to remove it.

The rear hole in the sight lines up perfectly with the rear hole in the Crosman breech. However, the hole was sized for a #6 screw rather than the required (for the Crosman breech) #8. Drilled out the hole with a #16 bit to gain the necessary clearance.

Installed an #8-32 bolt and nut to temporarily affix the sight to the breech.

Spotted right through the sight for the front mounting hole.

The supplied front mounting bolt for the T/C is a #6-48. The T/C sight requires extremely low profile bolt heads for mounting as they sit inside the housing. Rather than make a second bolt (I have to modify a #8-32 for the rear location) it makes sense to use the correct T/C front bolt. I drilled through the top of the breech with a #21 bit then started the #6-48 plug tap.

Finished the tapping by hand. I only had a plug tap in this size, so it made sense (well, to me) to through drill. Carefully de-burred the inside of the hole in the breech then checked the clearance for the loading bolt. Moves without a hitch.

Hole is nicely aligned and relatively inconspicuous should I ever remove the sight to use something else.

Almost forgot to enlarge the rear counterbore. A centercutting endmill in the drill press did the job in seconds. Not shown, I thinned the head of a #8-32 panhead screw for the rear mounting hole. The head is very flat and sits inside the sight housing nicely. Cleaned out the metal shards and set it aside.

I'm using a muzzle brake from the Crosman custom shop on this gun. It's threaded for a simple post sight. It's just a steel rod that threads into the tapped hole. Unfortunately, the additional height of the T/C sight will require a correspondingly taller front sight. A couple spare front sight inserts from an IZH-46M look like they're a good match. A scrap of aluminum will allow attachment of the blade to the brake. Coated it in dykem and found the center.

Lined it up with the center of the headstock by using a pointy indicator in the jaws.

Removed pointy and installed a 7/8" ball mill. Don't try cutting steel like this. 3-jaw chucks are not made to hold cutting tools. I took my time and made many fine passes on the aluminum.

The radius is a "close enough" match.

More dykem on the aluminum adapter. Sort of traced the sight blade into the front. As usual, I'm just winging it.

Milled about half the height away.

Angled the sides to make it interesting...

cut a shelf for the base of the sight blade...

Then drilled the #25 clearance hole on top for the #6-32 mounting bolt.

And drilled the front of the adapter with #40 then tapped the front hole M3 x 0.5mm to hold the sight blade.

A few minutes of clean up sanding and I had a nice satin finish.

Sight blade is bolted to the adapter.

Note the tiny shelf the sight blade sits on.

Adapter is bolted to the muzzle brake. The radius aligns it and prevents it from rotating.

Rear sight installed.

Compared to the LPA sights I removed, shooting targets is night and day better with these. All the corners are sharper and clearer producing a crisper sight picture.

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