Most springers have a loose guide ~ sproing ~ and are less than 100% consistant. In some the seal is damaged ~ smakksproing ~ and have very drastic velocity changes.
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The kicker are guns withwrong lubricants, thin and volitile ~ smakkPOWsproing ~ fire and smoke, burned seal and broken springs {or MUCH worse} with no accuracy whatsoever.
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After a tune, much different behavior ~thud ~ recoil is straight back, accuracyrivals a PCP, cocking is smooth and easy {exceptfor Genes' psycho magnum 1250} often able to shoot several pellets {sometimeswith better energy}exceptionally well.
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That has been my experiance anyway {YMMV}and I feel very lucky to call Bob and Gene myfriends, and sometimes Fritz evenlets them have a couple of hours to hang out and shoot bb guns with me. (http://www.getphpbb.com/phpbb/images/smiles/a_goodjobson.gif)