Upgrade guide options

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Cylinder Hole Location vs. Barrel Length Guide Chart
www.21stcenturyairsoft.com/cylinderguide.php

Spring Performance Guide Chart
www.21stcenturyairsoft.com/springguide.php

Motor Compairison Guide Chart
www.21stcenturyairsoft.com/motorguide.php

Battery Guide Chart - What does all this Mean
www.21stcenturyairsoft.com/batteryguide.php

Barrel Lenghts Guide Chart
www.21stcenturyairsoft.com/barrelguide.php

Gearbox Version Guide Chart
www.21stcenturyairsoft.com/gearboxtypes.php