The final chapter!
Unexpectedly, I came across another Crosman 451 that I was able to purchase in Canada.
I had no reason to disassemble my first 451 since it is working very well but now that I have another one in hand I would be able to confirm the fit of my last two iterations of the hammer.
This image shows both examples (my first 451 is the one with the rubber band on the grip). The slide is loose on the one I just received (some of the brass of the valve block can be seen). The cause is that the slide spring return doesn’t pull it enough forward. The tension can probably be adjusted.
Also the loading regions of both airguns are a bit different. It can be seen in the picture that, on the one I just received, the edge of the brass valve block interferes with the cavity of the pellet chamber. When loading, it is necessary to slightly fight the spring tension to let the pellets fall in the cavities and after testing the airgun with CO2 I can confirm that it cycled correctly.
At this point, it was time for the hammer fit verification. Over time I developed a technique to confirm that the mechanism will work without having to do a full reassembly. I put back the springs for the primary and secondary sears as well as the trigger spring then I visually check the relation between the parts by moving the hammer with my fingers. In this arrangement, all the pivot pins are not very stable but it gives a general idea how the components are moving together. Replacing the right side of the receiver over the other half will hold the pivot pins in their actual position to truly test their functionality.
Holding the frame with the right hand will keep both halves clamped together and allows the index finger to control the trigger. The left hand is used to replicate the hammer spring tension. Starting with the hammer forward, pulling the trigger has no effect (safe mode). Cocking the hammer and keeping the pressure forward (as under spring tension), the engagement in the full cock notch can be verified. Pulling on the trigger should release the hammer. Pushing forward on the hammer will mimic the firing cycle. After applying pressure against the firing pin, the hammer bosses should cam the secondary sear out of the way allowing the primary sear to reset (the tip will move up to contact the bottom surface of the hammer). A tiny click should be heard or felt.
Now it is time to mimic the blowback effect and verify if the cycle will complete correctly. Still holding the trigger pulled, the hammer is moved backward until it cocks (after cocking, a forward pressure is maintained on the hammer). Some tiny movement can be felt in the trigger finger when this happens. The next step is the critical stage. When the trigger is released forward, the secondary sear should also move forward and should slide in front of the primary sear to reset. Again a tiny click should be heard or felt (if it doesn’t happen the edge is still stuck underneath and the trigger would be in safe mode). When the secondary sear resets correctly, pulling on the trigger will meet some resistance meaning it is ready to fire and restarts the cycle.
This is how I confirm that my trigger system is working properly or not.
The picture shown below is the battlefield displaying the original components as well as the homemade brass hammer and the CNC machined brass hammer and sear.
I started my test with the one that was completely hand made. Unfortunately it didn’t pass. The results obtained were the same as my first iteration at the beginning of this long saga. To make it work, more material should be left around the teeth and the notch should be shaped to fit the tip of the sear and keep it angled properly. This will require patience and multiple assembly disassembly cycles to file the surfaces until they match correctly. Because I was trying to remove all the drilling marks I removed too much material and lost the shape that was on my paper template. I guess sticking closely to the guideline of the teeth (relief hole and boss) should give a better result and minimise adjustments.
This seemed to be confirmed when I tried the CNC machine hammer. I dropped it in place and it worked perfectly with the original primary sear. I could have left it at that but my goal here was to use a hammer and primary sear both being made of brass.
The test with both brass parts together failed. I knew the hammer was fine so the culprit was my sear. With a fine file I adjusted the bottom of the flat plate and chamfered the edge but it was not enough as the secondary sear was still hooked underneath. I filed a bit more of the vertical face where the hooking occurred and it finally worked.
The cycling was verified several times and once satisfied I reassembled the pistol.
This last photo has both Crosman 451 pistols where the steel and brass hammers can be seen.
It was a way longer trip than I expected at the start but the destination is finally reached.