Hi All,
My first time working on one of these guns.
this will be a long report so please tell me if its too much.
It may have to be broken up into two posts.
My son bought it, and put about 500 rounds through it, then brought it to me to see if we could at least smooth out the operation.
My first impression of this Chinese made gun was good materials, average fit and finish, poor finishing touches.
I put about 100 rounds through it using CPHP pellets.
It was accurate, with consistent groupings, but with the occasional erratic (1 in 10 or so) that would be out of the 1 inch circle I was shooting at from my outdoor bench at 25 meters.
435 fps avg on the Beta master.
Spring slap was very loud, and the break action was stiff and jerky.
Trigger pull was long and spongy.
Weight and balance was very nice, bluing very good as well.
Sights and scope were also more than adequate.
Time to come apart .
Take down:
Remove scope.
Remove 3 stock screws, no thread locker, one was very loose. bottom screw at the trigger.
Remove breech pivot locking screw, then the pivot screw.
Pull away barrel. (I will work on that after I review the compression system)
Place compression chamber in spring compression fixture. (Homemade)
Remove pin and locking stud (this was loose as well) release spring tension and disassemble.
Parts examination and repair:
Mainspring: Very rough, inside and out with lots of spurs from manufacturing.
Fix: using concave medium felt wheel coated with honing compound on bench grinder, I deburred the spurs and polished the surface. I did the same to the inside using a fine diamond cratex stick held in a cordless drill.
Piston: fairly good overall, with some minor burrs inside of spring hole,
Fix: Standard deburring tool and then smoothed with 1200X diamond file.
Spring guide: As it a stamped then formed the seem is uneven and burred, the black oxide finish is rough as well.
I file this even then polished on felt wheel. (you will see i like these wheels!)
Piston seal: excellent condition, nothing done to it.
Compression chamber:
This was the worst part of the gun, major burrs in all slots, extremely poor finish inside, even a heavy burr on the outlet port
Fix: deburr every thing, then diamond file to ensure all is smooth. 600X wheel cylinder hone to set a nice cross hatching in the chamber, and then you guessed it.. I turned a hard felt wheel to snugly fit the chamber and impregnate it with honing compound and polish the compression area until smooth., i mounted this on a wooden dowel, and used a cordless drill to spin it.
Before and after dimensions show I removed .0003" from the high spots in the bore and and almost nothing in the low areas using a digital micrometer on Starrett bore gauges before and after hone/polish operations.
I used a small diameter 82 deg. c-sink mounted on a carbon fiber arrow shaft to deburr the port, and gave it a little more for better air flow.
Trigger catch was also filed and deburred (not too much)
Lots of cleaning came next, first a magnetic retriever to pick up metal fines, then degreaser with a bottle brush to clean honing compound residue. compressed air to blow out loose particles, then a clean rag on a dowel to wipe clean, ( there was more to this process, but I shortened it to fit on this post)
Barrel time:
Breach had slight burrs left by the slight c-sink in the grooves of the rifling. I shaped a rubber diamond stick and honed this until the burrs fell off. (using a cleaning pellet to protect the fines from going into barrel) the muzzle was worse with the c-sink being heavily burred on both the lands and grooves. I fixed this the same way as above. ( I expect this was the cause of the occasional erratic shot) without even contact on exit, the pellet may tumble or spiral.
Breach seal was a little low in my opinion, so I made a .010" shim out of brass shim stock and an exacto blade to raise it. (Gotta get some leather hole punches for this!)
Reassembly:
2 drops of chamber oil in compression chamber. refit spring and guide, I brush white lithium on spring and guide, (not sure what is the right lube for this, but this has been working so far) Put the chamber back on the spring compression fixture and finish final assembly of the chamber.
I use blue loctite for the stud,
Clean barrel, I use .22 cleaning pellets pinched to fit snugly and bore cleaner to remove lead residue. then push more cleaning pellets through until clean.
Re-assemble barrel to chamber, tighten pivot bolt until i feel friction then back off until alignment of locking screw cutout.
Refit stock and use blue loctite on the stock screws.
Time to test fire.
Cocking was very smooth and quiet, firing into and old phone book shows almost no spring slap and very quiet operation. ( adding a sound meter to my wish list for future tunes)
Cycle the gun for about a 100 rounds to ensure all dieseling is gone, and the bore is coated with a little lead.
Time to Chrony:
Though I was hoping for more I had a solid 40fps gain with a 475 fps average using the same pellets.
If you want to know the speeds using alloy or flat nose please feel free to email me.
I'll add that to the bottom of my post.
Time to bench test for accuracy outside.
So something I did fixed the accuracy, most likely the muzzle fix, but in 50 shots, all went into the same 1" circle!!
Ran another 50 rounds through the gun and put it back up on the chrony.
another 5 fps gain at 480 fps avg. with very consistent speeds. total variation of only 8 fps.
Sorry for the long post, but I am looking for constructive criticism on all my methods and lubes, and any other tips I can get.
I'll try to add a pick of my bench and adjustable chrony and spring compressor.
Please feel free to email me at r.kelland@yahoo.com if you have any questions that need to be off list, or on here if you want to ask about where i get some of my supplies or how I developed my tools.
Note on the spring compressor, it has a quick release mechanism for after the spring is pinned so I don't have to back out the screw. (Yes I am lazy..lol)
Cheers all and thanks for letting me be part of this group.
Rick
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File comment: A work in progress the bench.jpg [ 114.99 KiB | Viewed 2347 times ] |
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File comment: Mounted on an old EQ telescope mount with a 2" stainless tripod adjustable in height and length to about 2' past the muzzle chrony.jpg [ 145.69 KiB | Viewed 2347 times ] |
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File comment: Fully adjustable for just about any chamber. spring compressor.jpg [ 202.16 KiB | Viewed 2347 times ] |
