Yes, it is possible to make your own broadheads. And a .308 casing is a good choice, as is a .38 or similar size, just so it fits (snugly, but not tightly) over the arrow shaft; cut off the closed end of the casing (the rim end) and flatten that end a little (not completely flat, or it won’t be strong enough) and cut a slot in that end, across the widest part of the now-flattened opening. Just make sure there is enough casing left to go on the arrow shaft.

Insert a triangular-shaped piece of flat steel as the blade. The blade can be made from an old bandsaw blade or any other thin, durable piece of steel, as long as the blade is at least 7/8 inch across the widest portion (usually the bottom, the “barbs”) and approximately 1 1/2 inches in length. Braze, solder or epoxy the blade into the slot (don’t try to weld it, or you’ll end up melting the brass), making sure it is centered in the slot and ***lined up*** with the casing; this is critical, or you will have a useless miniature sculpture. Sharpen the edge, glue the broadhead on the arrow shaft, and you have a servicable — although not necessarily world-class — arrow….

If you would rather have something more primitive, go to
http://www.primitivearcher.com/smf/index.php
and
http://primitiveways.com/
and ask questions/check out the articles. A lot more information in those two places than I could give you here.

Oh, yeah…. It’s fine to use a blow-torch. It’s safer in a lot of places, and easier to place the heat directly where it needs to go anyway.