Homebrew .177 cal build from Crosman 1377 and Crosman 140

Related Blog:
Part 2

I've been thinking about this build for a while. I am going for an accurate 10 meter pumper rifle in the 500 to 600 fps range. I would like to get to 500 fps in 2 to 3 pumps.
 Eventually I would like to build an air rifle completely from scratch. For now I'm happy building rifles by making what I can and using parts from air guns for the rest.
This build will be a combination of a Crosman 1377 a 1400 and a Daisy 953. The 1377 will donate its pistol grip, trigger group and hammer. I will build a pump tube and linkage based on the 1400 since it has a long pump stroke (8 inches). I'm using the Daisy 953 barrel for two reasons, I have one and it is a very accurate barrel. A 1760 or 2260 barrel would be easier.

I  found an old Crosman 1377 to use as a donor for this build. 

The pistol grip, hammer and cocking knob will be the building blocks for this build. 

I will be using a Daisy 953 barrel, 3/4" seamless brass tube for the pump and eventually I'll turn a breech out of aluminum, to get the build up and running I'll use a Crosman steel breech. 

I have a 1399 stock I'll add to it.

I like how Crosman pumper parts can interchange between models. Valves are all the same basic design. 

I have a few valves to choose from. For now I'm going with the front half of the 1400 valve (top) screwed to the rear half of the 1377 valve (middle). Replacing the front half with the 1400 valve will make it easier to go with a flat top piston on the pump. If this was going to be a .22 cal. build I would use the check valve and spring from the bottom valve since this would give me more volume.

The first round of machining on the pump tube went well and everything matches up.

A quick assembly to verify things are going to work. The brass tube is about .004" thicker wall than the original Crosman tube, making the ID of the tube a snug fit for the valve. I thought I might have to turn a few thousandth off the OD of the valve but it fits well as it is. 

Another trip to the mill and the slot for the pump linkage is done, along with the through hole for the linkage pivot pin.

I mocked up the pump linkage and adjusted the length of the piston for zero dead space. Then I needed to find out where the piston ended inside the pump tube with the pump fully open, a small hole is needed to let air into the pump.

I used the pump linkage from a Crosman 1400 as a model and cut the parts for my pump linkage from 1/4" flat bar. 

I added brass bushings to the pivot points and milled a slot for the link to fit in.

I wasn't sure how well the flat bar would work, but with it installed it is working fine. 

The 953 barrel has a shoulder about 3/4" long that I would have to cut off to fit the breech, then I would have to make a cutter to cut a new leade in the barrel so the pellets would slide in easily. While studying my parts I came up with a plan, cut the breech end off a 1377 barrel, bore it out to fit the end of the 953 barrel. 

It would have been easier to use a .177 cal Disco or 1760 barrel but I know this barrel was accurate on the 953 it came off of and I am looking for accuracy.

A trip to the lathe and I had the end of the 1377 barrel parted off, I bored a hole to depth to match the OD and length of the shoulder on the 953 barrel.  

After a good cleanup with alcohol I mixed up some JB Weld and glued the two pieces together. Some careful measuring was needed to get the 953 barrel centered in the leade of the 1377 barrel. The 953 barrel starts just past the transfer port.

 Not the best picture but you can see the lands and grooves of the 953 barrel are centered in the breech of the 1377 barrel.

While working on this project I was looking over the trigger group, the 1377 doesn't have a terrible trigger but I saw a few spots for improvement.

If you look close you can see the wave washer that keeps the trigger pressed against the side of the housing. The sear just flops around on its pin. I measured the gap at .028" between the sear and bosses that hold the pin. I measured the same gap at the trigger with the wave washer removed.  

In the picture below you can see the wave washer sitting on top of the trigger (left of the safety)

I made 4 brass washers/ shims on the lathe. Parting off .014" thick brass was easy enough but the washers came off cupped and I had to flatten them. 

It took some work with a file to get the shims to the correct thickness, but it ended up how I planned. There is a lot less slop in the sear and I don't have the pressure of the wave washer pushing against the trigger. I'm hoping this gives me a predictable trigger pull/ release.  

I was finally able to bolt everything together for a test run.

It took some tweaking and fine tuning to get everything working but the first tests are encouraging. The velocities are right where I wanted them.

For the Chrony tests I was shooting 7 grain RWS Meisterkuglen.

1 pump, Average velocity is 395 fps with an Extreme Spread of 6.9 fps

2 pumps, Average 550 fps with an ES of 4.1 fps

3 pumps, Average 646 fps with an ES of 8.0 fps

I don't have a handle on the pump linkage yet so it is difficult to pump more than twice. I had to find out what it would do at higher pumps so I fired once at 5 pumps and got 763 fps. 

Then I went for 10 pumps and got 815 fps.

The group bellow was shot from my bench at 10 yards during the Chrony tests, it is six shots at 2 pumps. I pulled the shot that is outside the group. Not bad for the first session, once I get a pump handle installed it will be more stable resting on the bag and easier to pump.

I plan on filling the open part of the 1399 stock with wood to make it look better and add some weight. 

I'm going to try adding a barrel band at the end of the pump tube and a weight to the end of the barrel. There is still plenty of work to be done but I'm happy with it so far.