GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: Ole Coyote on November 29, 2016, 07:36:48 AM
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I have read a couple of old posts on GTA concerning it, but they didn't seem to go very far, and I have seen a few outright success stories on YouTube. So, I am giving it some thought. Most of the YouTube videos are either .177 or .22, But one guy, (ww321 https://www.youtube.com/watch?v=4-14wcekq50 (https://www.youtube.com/watch?v=4-14wcekq50)), has a pretty solid, working .30 cal. He is achieving around 450FPS with just CO2. I am thinking .357, but would probably do one in .30 for starters just to see what kind of energy I could get out of it. He used a Spyder Victor for his base, but after a little research, I have found that all Spyders operate similarly. I believe Pirahnas work similar to Spyders. I looked at Tippmans as well, but the don't look quite so easy to work with. The good news is, most old Spyders and Pirahnas are fairly inexpensive & plentiful on eBay, in the neighborhood of $30.00. Here is a fellow in Chile with a finished .30 cal to give you some idea what it might look like https://www.youtube.com/watch?v=cKUMYcVCSd4 (https://www.youtube.com/watch?v=cKUMYcVCSd4) So, watch the videos and tell me if I'm crazy.....
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heres mine i still need to do more work on ,
its .30 caliber shooting predators at 290 fps.//I need to shorten the barrel a lot , but cannot bring myself to saw the barrel.What you will find with most models , is that the blowback is a massive waste of gas, and the more you mod the valve for power, the more gas goes torward blowback.. I retarded the blowback by removing the hammer oring.. im losing an honest 100 fps with the 19 inch barrel id assume
http://www.gatewaytoairguns.org/GTA/index.php?topic=117563.msg1131611#msg1131611 (http://www.gatewaytoairguns.org/GTA/index.php?topic=117563.msg1131611#msg1131611)
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HIGH PRESSURE .... in the valve and behind projectile ( Or lack of with PB markers ) is an issue followed by these guns NOT designed to do so either.
Typical pressure is that of Co2 / Regulated HPA of 800-1100 PSI.
PB markers valves are generally BIG so they can flow a lot of air at this lower pressure.
Hammer weight, trigger mechanics generally pretty light duty because there cycling load while fast is not very stressful on the parts.
RAISE the operating pressure to 1600-2000 ( Minimal for .22/.25 duty IMO ) and the hammer strike on these big valves needs to go WAY UP !!
This can mean MORE hammer weight and a lot more spring energy driving it. Trigger mechanics / sear have to strong enough to handle it.
Way valve is retained / held and the overall strength of the parts subjected to the higher pressure need to RAISE very serious SAFETY CONCERNS when doing so.
Can it be done ... ABSOLUTELY
Picking the right PB marker to fiddle with is important .... HPA is no joke !! and the last thing you want to create is a hand Bomb :o
Be VERY careful .... sadly don't think you will get much help here & likely thread of one being built will be locked simply because of the SAFETY and LIABILITY issues doing such modifications takes such PB markers into a realm they were never intended to go.
JMO ....
Scott
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If the valve is big and flows a lot of gas, why can't .22 be run on 1100 psi air?
People shoot .22 discos down to around 1000psi, I thought.
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the last conversion i saw on the yellow was a guy milling a slot for mrod mags , and running co2 for 700fps in 22 cal , SEMI AUTO !