Aperture Retrofit for the QB77

The Crosman 411 aperture sight was a nice addition to the QB77, but I wanted a larger diameter disc. The 411 disc is also too small in diameter to fit a rubber eye cup.



I was ready to make a new disc when I remembered that I had a spare aperture for a 10-meter match rifle.

I think it's an old Anschutz.

Size comparison. The Anschutz (?) has a weird M9.5 x 1mm thread. Then again, the Crosman 411 has a weird #12-28 thread...

After looking at the aperture for a while and making some comparisons to the 411 sight base, it looked like a fairly easy retrofit. Chucked the aperture into the 3-jaw to begin.

The ID of the threaded tube was exactly the right size to tap 1/4-28. Started with a plug type tap.

Followed with a bottoming tap.

Finished by hand with a proper tap handle.

A scrap of 0.250" drill rod about an inch long.

Faced both ends.

Turned one end down to approx. 0.212" or thereabouts.

Flipped the rod in the jaws and threaded the larger .250" diameter to 1/4-28.

Turned the rod around again and tapped the smaller diameter to #12-28.

Spotted.

And through drilled with a #29 bit.

Cut a small relief at the base of the #12-28 thread.

Scrounged a washer/bushing/spacer from a parts bin.

And bored out the ID to just fit over the exterior threads on the aperture.

It's strictly a cosmetic touch to cover the unused exterior threads.

Removed the elevation and windage plate from the sight base to test fit.

Greased the double threaded adapter and snugged it down into the aperture. Pulled the rubber eye cup off the HW 35E.

Anschutz (?) installed.

Looks exactly like what I was after.

Since I didn't damage or modify the exterior threads, the Anschutz disc can be still used on the correct base as well.

I'd still like to refinish the stock, get rid of the knurled nut with a recessed fitting , add a rear sling swivel stud, overhaul the rifle... All in good time.