I told you I was getting a bit airgun crazy again, didn't I?
Five or six years ago I bought a Slavia 631
spring piston air rifle at the Rickreal flea market. I only gave $40 for it, as I am a shrewd negotiator. It came with a Simmons scope but no iron sights.

The rifle looks too short because a couple of inches of barrel is missing. The previous owner must have had a problem removing the front sight., or dented it, or something. So he removed an inch or two...

Really, it's just too short.

I turned some random aluminum alloy down at the end on the South Bend and drilled it to fit the barrel. I was going to bore it exactly to size, but the drill I used cut just right at the diameter I was aiming for (which is technically a mistake, but it actually didn't matter).

Turning the OD (it's scrap so it was dinged and had spots of oxidation), grasped by the short section I turned previously and supported by the live center so as not to stress the thin tube section it's chucked by.

I moved the work over to the Jet 920, which has a DRO for cutting the grooves.

Groovy.

I drilled and tapped for some #10-32 set screws on the underside, but I should have used something like a 4-48, as I only got about two threads engagement, and the setscrews had to be ground down to about 1/8" of length. Poor planning just like the drilling, but it was a "for fun" project so I just winged it and it holds fine.

Now the rifle looks pretty, which was the whole point. I took it out and shot it a bit and the muzzle brake makes it easier to use, the longer barrel giving more leverage when cocking.
Here's the .pdf of the Slavia 631 manualA Czech airgun forumA Slavia 631 Tuneup