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Author Topic: Gamo Hunter 440 Tune / Modification  (Read 698 times)

Offline JS

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Re: Gamo Hunter 440 Tune / Modification
« Reply #15 on: January 15, 2019, 02:01:47 PM »
Hi Xyon, not a lot of time lately so no real progress..
« Last Edit: January 25, 2019, 09:21:06 AM by JS »
TX200 MKIII .177
Gamo Hunter 440 .22
Feinwerkbau 300s .177
Weihrauch HW80 .22
HW45 .177

Offline JS

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Re: Gamo Hunter 440 Tune / Modification
« Reply #16 on: January 25, 2019, 09:21:20 AM »
A little more work on the Gamo last weekend:

Finally got around to making a spring compressor and got it stripped down. Last one to open it was Youngs, which was confirmed by the red grease he uses.. And quite a bit of it..

Piston looks fine, and seal showed some scars. One large one on the rim was probably from removal of the piston - it was a very tight fit - may have also be sacrificing some efficiency due to the fit.



The piston has a light rub down with fine grit paper to give a bit of a polish to shooth out any burrs. Ove end is slightly flared which contacts the tube - this had harsh grinding marks which were polished smoother but smoothing out totally would make it a looser fit. It should be smooth enough for a nicer cocking and shooting feel, but enough texture to hold lube.

The seal was discarded and swapped with Custom Air Seals "Power Seal" which has a flat face similar to a Weihrauch seal rather than the ring type, which is said to be more efficient.
It was also much easier to push the piston into the cylinder - so lets hope this gives a little more added efficiency as well.



The original Gamo top hat is a steal one, loose fitting on both the spring, and in the piston - allowing for a nice twang when the rifle was shot. The rear guide was planned to be replaced, but the spring was actually not a bad fit here, so this will be left original.
I scrounged for ideas for a top hat replacement and found the delrin top hat & slip washer from a TBT tuning kit was a pretty good fit in the piston - very little play side to side so would keep the spring nicely in place.
A quick spin in a drill with some sandpaper sized it perfectly for a firm fit on the new spring.
 
The original spring was surprisingly straight, given it is 22 years old - this will be kept as a spare, but the new spring with mirror polished ends was installed.



The inside of the tube was given a polish with very fine paper to remove any burrs that were scarring the seal, everything was cleaned, then re-lubed and reassembled.

The rifle feels much better to shoot, no noticable twang & a nice quick cycle. Power seems good from the first few shots with nice depth into drypinedepthometer - around the same depth as the HW80, but I will give it a test at the range later this month, as well as do some strings over the chrony once the grease is settled in a little.



Fingers crossed it can now group smaller than 3" at 25 yards!
« Last Edit: January 25, 2019, 09:32:14 AM by JS »
TX200 MKIII .177
Gamo Hunter 440 .22
Feinwerkbau 300s .177
Weihrauch HW80 .22
HW45 .177

Offline Pauly5

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Re: Gamo Hunter 440 Tune / Modification
« Reply #17 on: January 25, 2019, 02:44:39 PM »
Nice project JS. Enjoyable reading
HW98
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Offline xyon

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Re: Gamo Hunter 440 Tune / Modification
« Reply #18 on: February 13, 2019, 11:30:53 AM »
Good to see you got it all back together.
You mentioned burrs on the crown, one thing I noticed was that if you go over it again with new paste and very light pressure when grinding, you should be able to remove the burr.
I just did this recently on a Gamo shadow that had a crown that a pellet would drop 10mm into the barrel, WTF, looks like it was made with a tapered reamer.

Another thing I just though of, which I haven't tried, would be to reverse the direction of the drill a few times during the process.