The dimple theory could easily be tested. Take a bullet and put some dimples on it. Use a round punch, or whatever shape you like. Reload a few of each type, size, depth etc. Then use some standard bullets and shoot them at a certain elevation, at a distant target. Then try the same distance with the dimpled bullets, at the same powder load and elevation. If they are faster, or hold their speed better, they should be higher on the target.