1377 and PM66 Junkyard Build

[bhh]

If you like to read about the works of art guys build here then you might want to click the "back" button now. This thread is about an ugly experiment.

Anyway, I bought a 1377 on sale last year. I hated it. The pumping motion is both awkward and hard for me.

Then I bought a Powermaster 66 at a pawn shop for $10. It had a rattle can camo paint job and cracked receiver. But it did have a rifled barrel and brass valve.

So I put the PM66 pump tube on the 1377 but gave it a quarter twist. Now I have a side pumper.

I also used the barrel. Yea, it's ugly, but you can't believe how easy it is to pump.







It was too cold to go to my shop with my lathe, so I made do with what I could find in my basement.  I'll later make a proper end cap/pump linkage/barrel support out of aluminum and a slimmer pump arm.

I sanded the valve to be a flat top and then cobbled together a double-stuffed piston. I'll turn an adjustable aluminum piston after it warms up.  I have no idea how this piston compares to a real piston, but the numbers with 7.9gr CPHP pellets are as follows:

3 pumps = 455 fps
4 pumps  = 510 fps
10 pumps = 710 fps
15 pumps = 762 fps

This is my first time modding a 1377 so I have no idea how these numbers compare. I suspect that I should have greater gains at the higher number of pumps.

To stuff the piston I epoxied four  No. 16 nails in the piston body and used silicon and the head of a brass screw to fill the conical valley in the piston seal. There is JB Weld in the Philips part of the screw head.



Other mods are a lightened valve spring and extended bolt probe. I smoothed the transitions and bored the transfer port to .140"

Accuracy? No idea. I have bad eyesight and need a scope.

So how do my numbers look?

[Rob M]

This looks incredible man , I built 2 sidepumpers over the years, and even the one with a 1 inch piston was easy to pump.. The numbers for the gun are pretty good  also.. How did you rotate the tube ??

[bhh]

This looks incredible man , I built 2 sidepumpers over the years, and even the one with a 1 inch piston was easy to pump.. The numbers for the gun are pretty good  also.. How did you rotate the tube ??

Thanks.

To rotate the tube I taped a piece of paper over the original 1377 tube. I used an x-acto knife to cut out the paper over all of the holes and slots. Then I put this template over the PM1377 tube and used it to show me where to drill the new holes. I used a dremel cut off tool to cut the slots.

[DanD]

That is very cool.

[Rob M]

This looks incredible man , I built 2 sidepumpers over the years, and even the one with a 1 inch piston was easy to pump.. The numbers for the gun are pretty good  also.. How did you rotate the tube ??

Thanks.

To rotate the tube I taped a piece of paper over the original 1377 tube. I used an x-acto knife to cut out the paper over all of the holes and slots. Then I put this template over the PM1377 tube and used it to show me where to drill the new holes. I used a dremel cut off tool to cut the slots.

 nice.. I actually cut and rewelded a 760 to make it a sidelever about 6 yrs ago ! .. I didn't have any machine tools

[bhh]

Added a front sight and two screws to stabilize the barrel, and thinned the pump handle.



I'm having a hard time with the crude peep sight and my trifocals, but did manage a dime-sized group at 10 yds.  I ordered a steel breech kit.

[Rob M]

nice ! .. crosman is probably  looking over your shoulder 

[bhh]

nice ! .. crosman is probably  looking over your shoulder 

 

I wish they would make a side pumper. It's easy and fun to shoot now.

Then again, any 12 year old kid can pump this one 15 or 20 times. I'd imagine that  parts would wear out quickly at that rate. Better for Crosman to have the user wear out. 

[Rob M]

nice ! .. crosman is probably  looking over your shoulder 

 

I wish they would make a side pumper. It's easy and fun to shoot now.

Then again, any 12 year old kid can pump this one 15 or 20 times. I'd imagine that  parts would wear out quickly at that rate. Better for Crosman to have the user wear out. 

good point..392 is a prime example