Gamo Swarm Maxxim 10x Gen 2
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Topic: Gamo Swarm Maxxim 10x Gen 2 (Read 651 times))
Heinzreudi Giger
Shooter
Posts: 6
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Real Name: Heinz
Gamo Swarm Maxxim 10x Gen 2
«
on:
April 25, 2021, 03:50:56 AM »
Greetings to All and Wishing You a Great Day Ahead.
I've just took up air gunning with a brand new but modest setup of a Gamo Swarm Maxxim Gen 2 in 0.22. Its been really good fun overall and I'm looking forward to picking up more morsels of knowledge and wisdom through this fantastic forum.
1) Got a Chrony recently and measured the fps and got 680fps with a 14.3gr CPHP. Youtube reviews point to 780fps with the same pellet. Official Gamo specs claim 1000fps with non lead pellets. Lead ones maybe 150fps less???
2) Took the piston out to inspect and noticed several score marks on the seal. About 0.2mm deep by estimation. Relubed with silicone grease and put everything back together and chrony again. Got 800fps and was in ecstasy with the results!!! Didn't last long through...It soon plateaued to 750fps...still good but not perfect.
3) Replaced the piston and breach seal with brand new polyurethane ones and tested again. Got anywhere from 630fps to 660fps. Something wasn't right I thought???
4) Decided to peer into the compression tube and noticed the scoring marks were on the walls of the cylinder. Bummer!!! Rigged up a pvc tube and drill with foam backed sandpaper at 500grit + 1000grit. Managed to reduce most of the score marks but one deeper score line remains. Used a sharpened bamboo skewer and can feel the slight indent when I run the tip across the score. Reinstalled the gun and tested nonetheless. It would not go past 660fps. Even when tested with a +25% gas ram, the numbers remain at about 660-680fps. If you notice in 2) above I got 800fps after the first dismantling. I reckon I installed the score lines directly into the score lines on the cylinder, hence producing an almost perfect seal.
5) Further inspection revealed that the piston tube had an raised metal area near the tip that was likely rubbing against the cylinder, causing the scores in the first place. Reached this conclusion after observing the score marks coming back after the first rounds of polishing. Bad luck with poor QC at the factory Gamo!!! Ground down that raised part of the piston and testing further but still not luck beyond 660fps.
WHAT I'M WONDERING IS...
How much further can I grind down the cylinder before the inner diameter is compromised and loses good contact with the the seal? So far estimate that its been total of 3 hours work with the drill (320grit & 500grit paper). The seal still feels tight when reinstalling. But I don't seem to be making progress on FPS in spite of reducing the score marks? Is there something I've overlooked? Must I grind down to the point where no more lines are visible?
Furthermore, I've ground down the skirt of the piston (the offending part is now ground to much smaller than the bore of the cylinder) to prevent it from scoring against the inner tube but fps seems to drop further to 650fps after that. Breach seals are OK as I did the paper napkin test to verify.
I'm in the process of buying a new piston as I feel that could be the root of the problem? What am I missing here???
Appreciate any help I can get!
Cheers,
Heinz
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Re: Gamo Swarm Maxxim 10x Gen 2
«
Reply #1 on:
April 25, 2021, 10:32:13 AM »
How much tighter did the new piston seal fit vs. the OEM ? some seals need sizing or they will rob power until worn in.
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Heinzreudi Giger
Shooter
Posts: 6
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Real Name: Heinz
Re: Gamo Swarm Maxxim 10x Gen 2
«
Reply #2 on:
April 26, 2021, 02:04:53 AM »
I tested using both the original piston seal plus the new ones. They all produced exactly the same results, ie. 650-660fps. Almost pulling my hair out at this point trying to figure out the root cause why the gun is not performing to specs. BTW...tried the +25% gas ram and same results, ie...650-660fps. Leads me to conclude that loss of compression is the cause...but where is the loss happening?
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Gamo Swarm Maxxim 10x Gen 2