Burrard gave the results of tests performed by Mr R W S Griffith in 1887, fired on a 12ft dia wheel running with a rim velocity of 200fps (approx 136mph). Immediately in front of the wheel was a steel plate having a 4' aperture with a thin paper pattern sheet across the opening. Mr Griffith was able to "Laboriously" ascertain the position of each pellet on the wheel in relation to the fixed pattern. Many years later P P Quayle fired shot charges down a darkened passage & recorded spark photographs of them against the wall behind. "Amazingly" they were in extremely close agreement, but after all they measured the same thing. Mr Griffith fired loads from a 2½" game gun of 42gr Schultz powder & 1 1/8oz of #6 shot as well as 2 3/4" loads of 1¼oz, powder charge not given. Loads were fired through cyl as well as various choke bored bbls. Mr Quayle's loads were not given. At 40yds result showed an average shot string of 3.6 ft for 50% of the shot, 5.2 ft for 75% & 12ft for 100%. Virtually all of this first 50% will be in the central core of the pattern, as well as most of the 75%. The remaining 25% will be composed of primarily the fringes & a few "Tailings". It was further found that guns bored to I/C or less choke loast had about twice the percentage loss in the 30" circle as compared to guns having ¼ choke or more. At yardages of 40 or less, with target moving at no more than 40mph, "FORGET" shot stringing. Beyond that range shot sizes must be increased to give adequate penertration, loads must be increased to give adequate pattern density, Tight chokes are required, giving a strong central thickening to maintain that density as range increases & then 10/20% pattern allowance must me made to compensate for stringing loss. Next you better judge your ability honestly, for you are going to have a small core of pattern capable of giving a killing pattern, surronded by a "Large" crippling area. A lot of things have changed, but these facts have not much changed since Burrard's day. If you want to study the best book ever written on shotgun ballistics, get a copy. You will likely find you won't have much use for any other. Firing on a fixed plate, careful study of the pattern, those which give the best most uniform distribution, within the central core will be likely to produce the shortest shotstring. One does not have to be able to reproduce every test ever made, but understand what those before have recorded, & apply their. Most always just buying one particular brand is not the answer, but finding the load which performs best in a particular bbl.
That's the conclusion I have drawn.
Miller
