To keep it legal, what is the percent of bore usually used on exit holes for best stability. In other words if I am making a muzzle brake or air stripper how small/big should I make it? Not sure what I am going to make but is .452 for a .429 too small?
Dan,The more open the airstripper bore hole, the more forgiving of misalignment - with lower risk of clipping, or "steering" the projectile.It is not just airstripper bore diameter that matters: If you have a tube at constant diameter, that is going to steer your projectile more than just a wall or a cone, each having a hole slightly larger than projectile diameter.For air stripping effectiveness, it is not just the diameter of the airstripper bore hole that matters. It is how far the edge or wall is from the muzzle. The further away from the muzzle the more effective the airstripper will be for a given through hole diameter. This, while the closer the "wall" to the muzzle, the less blast the projectiles sees directly after leaving the muzzle.There are many airstripper designs. They all work more or less. Some of them use a "wall", between one bullet diameter and one bullet length away from the muzzle; followed by a second wall perhaps two bullet diameters or two bullet lengths from the first wall. Which distance works best depends on the muzzle pressure. The higher the pressure when the bullet base "uncorks" from the muzzle, the more directly radial is the initial air blast. The lower the exit pressure, the more the air leaving the muzzle wants to follow the projectile through the air stripper bore. Obviously the pressure drops as air flows from the muzzle, so both extremes of air flow occur. To optimize distance from the muzzle, this is almost begging for an adjustable cone type stripper: https://www.pyramydair.com/product/hatsan-air-stripper-for-select-25-cal-hatsan-air-guns?a=4558If you provided more detail about the intended design, we could make more useful comments. I can understand it you want to design it yourself, and prefer not to share detail.