Over time those old chains tend to stretch; not a big deal as you can adjust the chain each time you fill up the gas tank. Be sure and keep the bar grove clean and free of sawdust as that tends to dull the drive links. You don't want to tighten that chain to much it will need a little play but do not over tighten the chain.
They don't really stretch, the pins and bushings wear out and the chain no longer fits the drive sprocket. This causes the drive sprocket teeth to wear into a hook shape, ruining the sprocket.
Are you referring to the drive links being sharp?
This might help:
http://www.cop.co.nz/brands/oregon/chain-bar-and-sprocket-maintenance-and-trouble-shooting-guide/drive-link-wear.html