I bought me some nice looking 3/8 birch dowels at Klingspors the other day and have been working on them. Without having a spine tester getting them right might be a little tricky. They also seem to warp easy while working on them but I can straighten them out with no problem. Will birch have warping issues even after they are finished?
In my limited experience, birch makes a fine arrow. I didn't have any warping issues with the ones I made, but I live in Colorado where it's dry most of the time.
Those 3/8"ers will probably spine in the 80s, so leave them long and use a heavy point.
Good luck1
I was on a Birch kick several years ago-it is a great arrow wood and will stay fairly straight. With dowels the spine will vary quite a bit, and you might try making a very basic spine tester using a couple of screws spaced at 26" driven into the side of your bench. Hook a weight-say 2 lb- midway over a shaft and mark the deepest part of the curve then you will at least have a basis for comparison.
I have been useing birch dowels that I sand down to 11/32. They do bend more easily than soft woods, but they are alot tougher. It takes a severe hit to break them. Bjorn right something to get in the right spine range is a must.