I tried sassafras a couple times, both broke. But like Pat, it was early in my bow building experience. Here's the only info that I've found on the wood;
SASSAFRAS is placed in this category with some reluctance. At .46, it tends to break on its back before taken cast-robbing set. Sassafras will become a fast, smooth bow if handled carefully. An ELB design makes the handle area do work, letting about 20% more wood store energy. At 1.5" wide and 76 or so long, with narrow outer limbs, it will be a durable, sweet-shooting bow. As with other tension-weak woods, a crowned English belly will offer some protection by allowing general and local set to take place, reducing back strain. If backed with light rawhide length or width can be reduced to that of a bow of typical .55 or slightly higher SG wood. All the sassafras I've seen has been thin-ringed, with a high percentage of early growth. This wood was thought well of in earlier times. Possibly better growing conditions allowed thicker-ringed, denser, stronger, more elastic wood. Possibly such wood grows today, in which case it would be rated here as a true bowwood. If given a choice select staves with thicker growth rings and low-percentage early wood. Sassafras is especially easy to work.
Tattoo Dave