Extension Cord For 220 Welder

I picked up my wire at a salvage-recycle center. When I was wiring in the outlet I was amazed at the small size of the wire out of the welder. Then I was informed that circuits for welders are based on the the duty cycle. Any way I wired in a true 50 amp circuit and used the recycled 8 gauge wire for the extension cord, better to go big.