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lampy · Veteran Member

I have had this project sitting for quite a while now. After a less than satisfying attempt at converting a 1377 to a .22 cal rifle it got me to thinking about this project so I dusted it off. It is based on a Crosman pumper. The pump linkage is from a 140/ 1400, the barrel is from a 2260 and the sear and trigger are from a 2100. The pump tube is 3/4" DOM tube. The valve is a combination of leftovers from my parts stash. If I remember correctly the front half is from a 1400 and rear half from a 2100. I used parts for the valve that gave me the largest volume I could get. I turned a flat top piston for the pump. It's still pretty crude but it works.
I have found the valve starts retaining air at 12 pumps. At 12 pumps I get almost 800 fps and the residual air in the valve after that shot will send a pellet out at 295 fps.
15 pumps gives me just over 800 fps and a follow up shot with the residual air at 428 fps..... I'm giving some thought to playing with the hammer spring and number of pumps to see if I can get two or more consistent shots from one initial pumping session of maybe 20 pumps.....
If that doesn't work out I'm more than happy sending .22 cal pellets down range at 700 fps with 7 pumps.
I consider this project a test bed/ prototype and hope to build a finished air gun from what I learn playing around with it.

5 shot groups with CPHP and CP from the cardboard box.

Mentolio · Veteran Member

Wow, that's cool! Nice work.

Slavia · Moderator

Very cool, and well executed. Should be indestructable - no paint chips or wood dents to maintain. Perfect for a test platform with frequent assembly/disassembly. I like the holes in the pump handle. They are decorative, but positioned right where the pads of your fingers go for grip. Could you post a photo of the rear of the breech? It looks like there is something there, but I can't make out what it is or does.

Good to see you use proper lubricants during assembly (can to left of the butt).

I have a 1377 project in the works, but with many false starts - I just can't seem to get inspired. Maybe because of the lure of trigger time, maybe because I'm a springer guy at heart. If you keep posting about your project maybe I'll be guilted into finishing it.

lampy · Veteran Member

Use of proper lubricants in the proper amounts can be helpful Thumb Up!

The holes in the pump handle were needed for traction and to lighten it up. when it was still a solid chunk of aluminum besides being slippery it would fall away from the pump tube after it was fired.

It's a bit hard to see in this pic, but I went with an M-16 or Crosman Challenger style "charging handle". It serves double duty, cocking the hammer and it is the bolt. I would do this differently next time and go with a more conventional bolt like is on the 1377.

If you think the trigger guard looks a bit crude or like an after thought, you are right. It was quickly hacked out and attached after I accidentally hit the trigger during the first shooting session and buried a pellet in the ceiling. In this pic you can see the cover that gives me access to the trigger and sear, makes it easy to get to for trying different mods.

Slavia · Moderator

lampy · Veteran Member

I have been giving some thought to another build.... Combine my Frankengun with a 1377.
I would use the pistol grip, trigger and sear along with the hammer from a sliding breech 1377. Build a pump tube from DOM brass tube. I have a barrel from a Daisy 953 that I would use.
Add a 1399 stock and this will be a 10 meter rifle, shot mostly from a bench. I'm hoping to get 500-600 fps with 2 to 3 pumps
I have a vintage 1377 on its way Smile