Hi Everyone, 3/8" or 1/2" steel balls? Why? I will be calling royal steel ball very soon.
It really depends on the strength of the bands you're shooting, your drawing style, what you're shooting at, and the range you're shooting at.
I personally shoot medium to medium-heavy latex bands (12-16 lb range), gangsta (horizontal) style, and I mostly shoot short and medium range targets. I find that 3/8", 7/16" and 1/2" steel all work well, but each have their caveat in that band range.
3/8" steel will give you a bit more speed, but because it's a lighter shot, it doesn't take the fullest possible energy advantage of stronger bands, so it'll tend to magnify any 'issues' you have with your grip and release technique, and the result is an increased tendency towards bandslap and a less accurate grouping. However, it's fine for lighter bands, and butterfly style in particular. Smaller shot generally gives a flatter arc, longer range, and (because of it's smaller size) improved penetrating power.
1/2" steel is a heavier shot (+142%) whose increased mass will offer the twin advantage of getting a slightly improved energy efficiency from your bands, and it'll tend to compensate for any grip/release issues you may have, resulting in slightly improved accuracy, and increased overall striking energy. The drawback is that for the same energy imparted, larger shot will move a bit more slowly, and have a steeper ballistic arc, then lighter shot ... which doesnt matter at short range, but becomes increasingly significant at medium and long range.
7/16" (44 cal) steel is a good all-around compromise between the two. It has the advantage of increased mass (+62%) and improving the energy efficiency obtained from your bands, while not being as heavy as 1/2".
I generally prefer 7/16 & 1/2 for the type and style of shooting I do. I actually keep all three on hand, and will pick the ideal ammo for whatever band I happen to be shooting at the time ... I have a good backstop that captures my ammo, and I built a sorter that separates them, so mixing up my ammo use is not a problem.