.575 is a very tight constriction. Here is a quick synopsis on chokes and as you will see in the article they don't even mention one that tight. Many people think the tighter the choke the better the pattern, but that is not really true.
* A typical factory 12-gauge barrel measures about .724 inch. * Many popular turkey guns come with chokes with a .665 constriction, which shoots No. 5 or 6 lead shot extremely tight. * Super-tight turkey chokes — such as those with .660 constrictions — shoot small shot, such as No. 6, best. * Chokes with larger constrictions, such as .680, usually work best with larger shot — No. 4 or 5 — or in shotguns with back-bored barrels. * Hevi-shot produces the tightest patterns through chokes with constrictions of about .675. In testing, Hevi-shot fired through a special .675-constriction tube produced an average pattern density of 94 percent. Hevi-shot fired through a factory full choke (.691 constriction) produced an average pattern density of 88 percent in a 30-inch circle at 40 yards. * Hevi-shot fired through standard improved-cylinder chokes (.718 constriction) produced an average pattern density of 70 pecent, which is the industry standard for a “full” choke. When Hevi-shot is fired through chokes tighter than .665, pattern density begins to deteriorate.
Last edited by Topgun 3006; 03-04-2015 at 11:32 AM.