New Crosman 1377 are under power - here's how to fix them.

[Biker_Bob]

I have an early phase III 1377 (bolt action) pistol - I've converted it into a carbine with a QD shoulder stock and it's very good indeed. It's making 5.7 ftlbs

I bought a brand new 1377 (the one with the black plastics). It was doing 3.2 ftlbs! It felt the same to pump, same effort required but it just made that power. I'd done some reading and seen mention of reduced transfer port sizes. I did some investigation and sure enough the transfer port was much smaller than in the older gun:
http://www.flickr.com/photos/30750063@N05/8531486545/
Here you can see the port from the old gun on the left, the small port from the new gun on the right and the new replacement transfer port I got off an internet auction site
With the bigger port fitted I was disappointed to see that the power had only gone up to 3.4 ftlbs.

More work needed, I took the valves out of both guns for a look.
http://www.flickr.com/photos/30750063@N05/8532593980/
Here's the problem - the valve on the left is from the new gun and you can see that there's a bleed hole drilled in the back of the valve. When the gun is fired some of the air is vented back into the hammer chamber, thus reducing the power.

Here's the front of the valves, I'd read about the shape being different on restricted guns, but these are the same.
http://www.flickr.com/photos/3075006...n/photostream/

This is a plug I made from an M3 screw, I cut it to length and slotted the end so I could drive it in with a screwdriver. The hole in the back of the valve is 2mm I drilled it to 2.5mm and tapped it to 3mm. I stopped tapping just short of completing the thread, that way the screw tightens itself as it bottoms out. I used some Loctite too to hold it in place.
http://www.flickr.com/photos/3075006...n/photostream/
http://www.flickr.com/photos/3075006...n/photostream/
http://www.flickr.com/photos/3075006...n/photostream/

So, with the gun re-assembled it's now making 5.7 ftlbs! Woohoo!
If the power proves to be a bit close to the knuckle the fall back position is to refit the smaller transfer port and then tune the diameter. For reference the small restricted port measures 1.9mm and the large unrestricted one is 3.0mm

From the reading I've done it appears that the new pistol I bought is a Canadian spec one, they have lower power limits than us. Maybe Crosman decided to rationalise the range and make just two variants - full fat and Canadian restricted and since the Canadian version is legal here too we get these weedy pathetic emasculated versions.