Air Gun Home :: View topic

Slavia · Moderator

I know, I know - another epic saga. I'll try to get this one done before Alstone's eyesight goes.

I had the 1377, a 30 year-old Tasco 2.5X30 scope, a Sheridan intermount, and a 15" barrel from a garage sale find. Time to use up the junk parts. It will remain a pumper, with perhaps a few valve mods to go with the longer barrel.

The barrel is rifled, clean, and shiny, but it had the overmolded plastic breech attachment. It's the right diameter, but I'll have to create my own transfer port. I'm thinking a carbine conversion:

For a finish I'd like to try satin poly over black paint, with bed liner in the appropriate grip areas.

This is where I'm headed:

Just for curiosity, the original 1377 barrel is rifled, but doesn't appear to have much (if any) twist. Are they all like that?

broommaster2000 · Moderator

Liking the design, as we've sort of come to expect from you. Mr. Green

I'm looking at a short 2240 barrel now. It doesn't seem to twist much either. Neutral

AirGunEric · Site Admin

Hard to tell from your picture- but the barrel twist rate does seem rather low- let me check a new 1377 barrel later tonight to compare. Most Crosman barrels, however, do have more twist that what I can see in that picture...

Slavia · Moderator

The muzzle brake came from the county recycling center. It was a broken plastic tube from a shop roller rest. I drilled it out to match the barrel, shaped the ends freehand on a belt sander, ported it in the drill press, and smoothed out the dings with Scotch-Brite. Both the mounting screw and the adjustable sight pin are threaded into brass inserts, super-glued in place and ground down flush with a Dremel and file.

The sight pin isn't necessary with the scope, but I decided to add it while I had the drill press set up - just in case. It is the remains of a brass thumb nut and 8-32 screw, turned in a portable drill and shaped with the Dremel:

The scope is a 30 year-old 2.5X Tasco. Not rated for springer use, but it should work on a pneumatic gun. While playing with it I noticed it was pretty blurry, so I checked the parallax - it was corrected for 12 yards. I made a tool from a length of hacksaw blade (it engages the two little notches in the objective assembly so you can tighten/loosen the objective bezel without unscrewing the lens).

Then I started on the glare shield (PVC pipe). I noticed as I was working it on and off that the objective lens turned, so I thought, why not use that? It's now adjustable. I set the parallax correction at 50 yards with the lens screwed all the way in, and it will focus down to 10 yards when unscrewed 1.5 turns. (12 turns unscrews it completely.) The PVC pipe is shimmed against the scope with padded toolbox drawer liner, held in place with double-faced tape. The rear shim is lubed with PTFE grease so it will slip:

The labels are computer printouts waterproofed with clear packing tape on both sides, held in place with double-faced tape. The scale is red and green so I can tell where I'm at - it bottoms out at 50 yards, red is the first turn, and green the other half turn.

The barrel is sheathed in vinyl tubing, just to give it a "thicker" appearance. Instead of boring out the 1377 barrel band I used a 760 band, but with a machine screw and turned-down "T" nut instead of relying on a wood screw in plastic to clamp the barrel. The new scope cap is the "ears" from the original (smaller) cap super-glued to the cap of a spice jar. It got new elastic bands also, courtesy of a bicycle inner tube:

Slavia · Moderator

The adjustment screws on this scope have no limit stops, so they just unscrewed. I removed the springs and pawls so they wouldn't get fried when I soldered on the knob extensions:

I sliced through the head and cut off the threads of a 1/4" bolt to make the extensions:

After filing through the plating to get to bare brass, I soldered on the extensions:

For the elevation knob, I turned down a Radio Shack knob to fit inside a piece of PVC pipe (again, using the drill and Dremel with part of the bolt as a mandrel):

Another knob super-glued to the PVC with a threaded brass insert for the setscrew goes on top of that:

A little paint and some labels and it's done. The yardage calibrations are a wild guess from Chairgun - I saved the template so I can re-calibrate with field data:

I had one large turret cap that I found at the range, so the azimuth knob is smaller to fit inside. I used a sleeve cut from one of the original turret caps to cover up the elevation turret threads.

Alstone · Moderator & Site Supporter

Here we go again! I going to try and keep up this time, other wise it’s like missing an episode of your favourite soap, after a while you haven’t got a clue what’s going on. Question

For a start I’m impressed with the mods to the scope turrets. I surmise that you learned the trade of cobbling things together when you went to the moon on Apollo 13? Mr. Green

Joking apart it looks like your off to a good start. Thumb Up!

Al

Bozo · Veteran Member

Slavia, your creativity and competence amaze and inspire me. I really need to get my lathe and drill press unpacked and set up.

Slavia · Moderator

Mark5043 · Silver Status Member

Slavia · Moderator

I could have gone with a dovetailed aftermarket breech, but I had some parts laying around that I wanted to use. The Sheridan intermount clamps securely, but it required a little adjustment. A Sheridan has a 0.343" (measured) O.D. barrel soldered on, so the mount sits butted against the pump tube. Not only is the Crosman barrel bigger at 7/16" (0.4375" nominal, 0.4370" measured), but it sits above the pump tube (in fact there is a plastic spacer). To keep it from twisting the barrel against the barrel band or tansfer port, I added setscrews to either side. (The screw shown is a prototype - it will get real setscrews flush to the mount.)

A scope mounted directly on the intermount would sit so low as to make it impossible to load the gun. I had the upper half of a Gamo adjustable one-piece mount, plus two regular scope rings. I cut the clamping portions from the two rings and bolted them to the Gamo mount. This in turn clamps to the intermount, and gives plenty of finger space for loading:

Some of these pieces look pretty rough, but they'll be painted or blued after the gun is happy mechanically.