Aww, that's like asking how wide tires should be? Or how much does a dog weigh? The Padre Island bows... the originals I measured, were 1.5 inches wide and high at the lock, and given the size of the prods, I would estimate they drew at least 300 lb... maybe 400. Made of oak, if you wanna know. Given decent wood, you can make a crossbow stock that narrow. The big square Flemish Arbalests, like the one from the pattern in Payne-Gallwey is approx. 1 and 5/8 inches wide at the lock, and the same at the head... but the stock is pretty tall at both head and lock, with substantial steel lockplates. The skinny 14th century German bows, typically seen with wood or horn-sinew prods appear to be between 1.75 and 2 inches wide at the lock. Stout German horn/sinew or steel bows from late 15th century are substantially thicker at the lock... maybe 2.5 inches wide and high. The short/fat German sporting bows of the 16th century are often close to 3 inches wide at the lock... but they do use very strout, heavy steel prods. So it really depends on what sort of bow you're trying to replicate. But the good news is, if you use decent nut or fruit woods... oak, cherry, pear, walnut or some such, you can build a pretty slender stock that will still take the load, IF you make it as close to the original design as possible. Vary the pattern at your own risk... those old guys knew their materials. And have fun stormin 'da castle. Geezer.