Above is the 1377 with the original plastic breech and brass bolt handle and rather cheap 459MT scope mounts designed to "clamp" on the barrel.
The scope was the $10, Leaper red dot and I found that the barrel would rotate with very little effort.
Here is the 1377 with the new Crosman all steel breech installed. VERY solid mount with the 3/8" dovetail scope mount built into the top of the breech. Plus there is an allen head set screw that hold the barrel from moving.
I have tweaked the trigger spring a little but wasn't to sure how far I wanted to compress it until I shot the gun enough to learn the trigger.
Just had to throw in one photo of my Yuengling pellet trap. There are 3, dollar store rag throw rugs folded inside with a couple layers of cardboard. Oh yeah, it was fun emptying the case too.