With any doweled material there is going to be a wide range of spine weight and physical weight, even with dowels that are made specifically for arrows. When you buy store bought shafting the separation work has already been done to a certain extent. With regular doweling material their intended use is not for arrows but there will be a certain quantity of them that will fit into that category. It is up to you to find out which work best for you for your arrow making.
A spine tester is to measure the deflection of a shaft with a specific amount of weight added to it's center. This is done with industry standards in place. The deflection numbers(in thousandth) and the amount of weight hanging from the center are only to achieve the industry standard and not necessary to find arrow shafting that will work as your arrows. You don't need a "spine tester", per se to make good arrows. If you have a commercial arrow that works well for you, place 2 nails in a wall 26" apart. Hang a weight from the center of the shaft and mark the deflection. Any shaft that bends to that point with the same weight added will be in the ball park. Some will come out stiffer and some will come out weaker. Even these "odd balls" can be adjusted to the correct spine by reducing their length(to increase spine weight) or by adding extra inches over the "standard" 28" mark to decrease spine weight as well or by reducing their diameter by scraping, planing or sanding. You can get in the ball park when you are selecting the store bought dowels by a simple bending them in your hands and feeling their strength or weakness.
When making hardwood shoot or sawn stock arrows generally you will start out with a blank that is possibly twice the diameter of the desired finished arrow. You reach the optimum size, physical weight and spine weight by working the shoot down with a plane or by scraping and/or sanding.
Lots of arrows are made with birch dowels as well as other types of wood. Birch makes very good arrows.
