rp181 wrote:Wouldnt the mass go up exponentially. As you add layer after layer, theres more surface area to cover, increasing more and more weight.

Mass goes up as the cube of the radius. The volume of a sphere is 4/3*Pi*r^3. So, if you double the radius you increase the volume by 2^3=8. If the material the two spheres is made of is the same the mass goes up by the same amount.

The cross sectional area goes up as the square of the radius. Area=Pi*r^2

As you increase the ammo and barrel diameter, and if you are using spherical ammo, then the mass of the ammo goes up much faster than the cross sectional area. That means it takes higher pressures to get the larger ammo up to the same speed as the smaller ammo from a smaller barrel. This only applies to spherical ammo, the relationship is different for other shapes.

In ballistics, there is a realtionship called the sectional density; mass/(cross sectional area). Ammos with high sectional density carry farther than ammo with low sectional density. Compare a golfball with a ping-pong ball. About the same areas but the golfball is much more massive and will carry farther for a given muzzle velocity than will the pinp-pong ball. Sectional density is also relevant when you are talking about internal ballistics (the ammo moving through the barrel). As you change the sectional density the acceleration of the ammo changes. Higher sectinal densities means the ammo accelerates slower, all other things being equal. Since sectional density is

mass/area = 4/3*Pi*r^3*density/Pi*r^2 = 4/3*r*density

So the sectional density changes with the radius and that affects how much pressure you need to get to a particular muzzle velocity.

I believe if you maintain the same sectional density as you scale the gun the muzzle velocity should stay the same, but we are neglecting differences in friction, valves, CB ratio etc.