Air Gun Home :: View topic - The Canadian 1377 Crosman could have built, EH?

rsterne · Moderator

About 6 weeks ago, I wrote a thread on "The Canadian 2289 Crosman could have built, EH?" .... That experiment was pretty successful, so I ordered a 10" .177 barrel from AirGunEric at scopesandammo.com and took the same approach.... Wink

I knew this wasn't going to be as easy, but I had never had a 1377 before, and really had no idea what to expect.... I used the same 2289 chassis I did for the last gun (plugged bleed and F-T-P) and the first surprise was that the 1377 with 10" .177 barrel had nearly the same performance as the 2289 with a 14" .22 barrel.... I guess what you gain from the lighter pellet, you lose with the shorter barrel.... Shocked

After establishing a baseline, the first step was to change out the 1377/2289 hammer spring for one from a 2240 as I did in the previous experiment with the 2289.... The gun immediately began retaining air sooner (the desired result), but the velocity was still too high to be non-PAL.... The next step was to fit a lighter hammer as in the pic below:

This hammer was made from a stock 13XX hammer by turning it down to 3/8" OD for most of it's length, and shortening the back to just outside the cocking pin hole.... I managed to reduce the weight by 50%, from 42 grams to 21 grams.... The lighter hammer helped, but the velocity was still too high, so I pulled the valve out and fitted it with a "long" check valve and spring as used in some of the old brass valves with the brass exhaust valve.... This check valve is over twice as long as the short one in the present aluminum valves, and the spring is shorter to compensate.... The result is a significant reduction in the internal volume of the valve, from about 1.6 cc down to about 1.2 cc (ie 25% less).... Cool

Now I was getting close.... the smaller valve did exactly what it was supposed to do, cause the pressure to rise quicker with each pump stroke.... Smaller valves do that, at the expense of top-end performance, but I didn't want that anyway.... Shocked

.... (Note; an even smaller volume valve would be better for this application in .177)....

In order to reduce the velocity further, I had to reduce the hammer spring tension even more.... Rather than cut the spring by trial and error, I fitted a Rear Velocity Adjuster (RVA) and simply backed off on the preload until I got the gun under 500 fps no matter how many times you pump it.... If Crosman were building this gun, they would have to custom tailor a hammer spring for it, a pretty simple matter.... so that you couldn't adjust it back over 500fps.... Rolling Eyes

You can see that you can never get the gun to shoot over 500 fps.... It gets to 460 fps in just 5 pumps.... but at 6 pumps it is retaining air and producing a 2nd shot.... The velocity on the first shot peaks at just under 500 at 7 or 8 pumps, and then starts coming down while the 2nd shot gets stronger, until it peaks at 11-12 pumps (again just under 500 fps) and you start getting a third shot.... This process repeats, with the first shot getting weaker, the second shot hitting a plateau and eventually decreasing.... and the third shot getting stronger until it also plateaus at just under 500 fps.... By that time, the first shot is dropping fast, and it is so quiet you can tell that you are approaching valve lock.... so I didnt test any further.... Embarassed

I know that every gun is an individual, and if you did these exact same mods you might be just over 500 fps or down at about 450 fps.... but it looks to me like it would have been a pretty simple thing for Crosman to build a Canadian 1377 that would stay under 500 fps and yet reach that in just 5-6 pumps.... If such relatively simple changes could keep a F-T-P equipped 1377 "legal".... think what Crosman could have done if they had bothered.... Since we all know that's not going to happen.... at least now you have the information on how to keep that F-T-P / plugged bleed 1377 non-PAL.... Twisted Evil

Here is a picture of the resulting 1377, complete with Red-Dot, similar to a Walther or NcStar, with multi-reticle:

I made a custom mounting plate so that a sight with a Weaver base could be attached to the Crosman steel breech.... It's really very simple, just a piece of 1/8" aluminum plate the right width, with a dovetail milled into each edge to match the Weaver slot dimensions.... There are two holes drilled and countersunk in the plate, and matching 8/32 holes drilled and tapped into the top of the breech, using short flat-head screws that don't hit the barrel.... I even drilled an extra hole in the plate so that I can remove the barrel retaining set-screw by only removing the sight, I don't have to remove the plate.... Cool

Pistol Field Target, anyone?.... Twisted Evil

Bob

AirGunEric · Site Admin

Hey, that's purty nice- three shots around 450fps at 13 pumps! You could shoot quite a few targets on the cheap like that!

Why does it take all the "amateurs" to do this sort of engineering and not the people hired by the manufacturers?