I decided to try a new sear spring case and spring. I found a spring case and spring at Popperts. The case threads looked really good. I had a lot of fail to load at the range before the case problem came up so I decided to replace the carrier/cartridge stop assembly with a factory new assembly from Numrich.
I had little hope the new spring case would work because the threads in receiver looked practically gone. But I had it in my head that I was going to get this thing shooting. What ever it takes.
I finally got the spring case and spring. I got the new case threads to start in the hole. Just enough to hold it there. I tried installing the spring through the receiver. Just as I decided that was not going to work it shot out into the air and straight down into the corner pocket of the pool table. Two days looking through the table for that spring. Gone, nowhere to be found. I had to order another spring.
I was sitting there frustrated with it all, looking on Numrich for another spring. I happened to look down at the 550-1 schematic and just happened to notice a part. A part that was missing from my gun. A receiver plug retainer. As many times as I looked at that schematic. After taking that gun apart and inspecting each peace. I never noticed it was missing.
So, I ordered a new spring and retainer. Numrich did not have a original retainer but did have a reproduction. Two weeks later I got the parts. Time to try again. Still did not really think the new sear spring case would hold in the stripped receiver.
I found that a peace of 1/2 inch copper pipe was near a perfect fit to slip into the receiver and hold the sear down near the bottom of the receiver where it needed to be. That would leave me both hands free to try and install the spring and case. It was really not that hard to compress the spring and start the threads of the case. It screwed down really tight.
It was holding hard.
Took the gun to the range. All worked perfect. No fail to eject. No fail to load. No fail to fire. All perfect.
Except, The new plug retainer did not retain the plug. Found a new "original" retainer at Classic Firearms and parts along with a deflector. Now my 550-1 is complete and working perfect.