I picked up the "three pack of TS-45s for nearly no money" not long ago, and have had great pleasure in bringing the details of these low powered but accurate shooters up to a functional condition.
One of the aspects that needed significant attention was the heavy direct sear trigger. Inspection of the latch and sear on each of these rifles confirmed that the metal was not near hard enough. In all cases, a file would cut both components.
I purchased some "Cherry Red" hardening compound and processed each of the three rifles as I had them apart for various reasons. The first two are really working great, and I thought I might really harden up the last of the three.
Well, the original latch rod must have had a little carbon in the mix, maybe they stirred the pot with wooden sticks, because after doing the hardening process, a round of test firing was called short as the gun would not cock.
Disassembly showed the the nib had broken off the piston latch rod just where you would think it might. I never thought I would need to temper the Chinese steel. Underestimation!.
Well, I've been looking for just this excuse to make up a new piston assembly, but as I was picking through the stock box, an entirely different idea passed through my head. Fit a piece of HSS or Carbide at the latch sear interface!.
Since I didn't feel a first try prototype was worth the effort required to shape carbide, I grabbed a short bit of 3/8th square HSS. Squared it up on the surface grinder. Prepped the broken latch rod square with the same machine. Cobbled together a jig to hold everything in lignment while I brazed the two together. Viola! Two had become one...composite construction! Hybrid functionality!
When the parts cooled down (Slowly ;_) Final shaping of the latch end was done. First with files to remove the extra brazing rod, then with grind wheel followed by slip stones to shape up the new end.
(Hard as..ahh...err...High Speed Steel! )
It sure is easy to maintain a square sear face geometry this way!
After it's all back together, the trigger action is much improved again. Hard steel on hard steel is a good combination.
I'll need a few hundred shots fired before I claim the entire effort a success, but so far...It's GOOD!