I've had the honor and pleasure of knowing my wife's 2 sons for 16 years. The younger, Jeff, is now 32. He got this Summit last year. When new, it would shoot 5" to 8" 5 shot groups at 20 yards. After that outing, he let it sit, in disgust, for several months until I could talk him out of it.
I then did the following:
Replaced the trigger with the GRT3
Deburred the main tube and lightly cross-hatched the compression chamber with 320 grit paper.
The barrel had a crescent shaped burr on one side of the crown. I chopped off 1/4" of the barrel and recrowned it in the lathe.
Rebuilt the hinge using brass washers and a hinge bolt with a locknut. I turned the bolt from a 5/8" steel bolt and cut the stock to be able to adjust it without disassembling the rifle. After the attached picture was taken, I tapered the outer 2/3 of the nut for a more finished appearance.
Replaced the breech seal with a shimmed o-ring and the piston seal with the best of 4 OEM seals I ordered from Crosman.
For the spring guide, I wanted UHMWPE, but avoided compressive loading by replacing only the section of the guide within the spring.
I cut off just the steel portion of the spring guide that's exposed above the spring bushing. I then turned a stepped guide rod with a large end to fit the ID of the spring and a small end to slide tightly into the original guide and bushing. I cross drilled the entire assembly at the base and pinned it together. (wish I had taken pix of that)
Polished the spring ends and added bearing washers
Assembled with Honda moly grease, heavy tar, moly/oil mix where indicated
The cocking roller was eating into the stock. I made a bearing surface for the roller to ride on out of 1/8" key stock. Note the extended "tails" and the glue pockets cut in the stock to receive them. Also pictured is the adjustable router guide I made for the Dremel.
I epoxied the track in place with liquid steel.
It now groups 5 shots into one inch at 20 yards(just not with me shooting it-lol), and it's SO smooth.
It took a few months to convince Jeff to try it again.
Check out Jeff's first kill with it on Hunting Gate.
