I ask this question as it relates to patterning a turkey gun, please read the following before answering;
I've been patterning shotguns for over 35 years and turkey hunting almost 20 years now and everytime I go to the pattern board before spring turkey season I just chuckle! Over the years I've read dozens of books on the subject of shotgun patterning, some that date back to the 1920's, and frankly none of them cover "turkey patterns" and I suppose that is because our sport is young compared to waterfowl or upland game hunting.
40 yards and a 30" diameter circle have been an "industry standard" since the first shotgun barrel was "choked" in 1870....prior to 1870 shotguns were cylinder bore from breech to muzzle for the most part! a pattern percentage system was put into place to determine full, modified, imp cyl and cyl chokes or 70, 60, 50 and 40 percent respectfully. This method (30" @ 40yds) is ideal for waterfowl, upland and clay targets....anything that is "flying"! In fact, a lot of waterfowlers shoot "flying" birds at 40 to 50 yards on a routine basis but are turkey hunters going to those distances regularly. If you watch a lot of turkey hunting shows or video's they are inside 20 yards nearly 90% of the time!
The NWTF and their "Turkey Hunting Safety Task Force" ironically determined that 40 yards is the maximum distance or range to ethically and cleanly kill a turkey with a shotgun. these are their words not mine, so don't flame me on this one! In addition, the NWTF has suggested that ANY turkey combo (gun, choke, load) that can place 100 pellets inside 10"dia @ 40 yards is an "ideal pattern" for turkey hunting. Adding an internal ring or diameter to the 30" circle was also done decades ago but most shotgunners used a 20" internal circle rather than a 10", the smaller diameter came about by those seeking a center dense "turkey pattern". Surely the NWTF isn't suggesting that a 28, 20, 16, 12 or 10 ga are ALL capable of putting 100 pellets in a 10" circle and ALL are capable of killing turkeys @ 40yds?!?! (you don't have to answer that, i'm just poking fun at our friends at the NWTF)
So back to my original question.....what's so magical about 40 yards?
1.) Is it because we use 40yds from the "industry standard" derived to measure shotgun choke percentages?
2.) Is it because someone said it was the "effective killing range" for turkey hunting?
3.) Is it because as American's we think "bigger is better" or "further is better"?
4.) Is it because the ammo industry wants to sell us more and more ammo to test each year in search for the ultimate "pattern"?
I think the answer is #1 and we've fallen into the trap of "pattern percentages" not "pattern density" or uniformity at a distance in which most turkeys will be harvested! The turkey shotgun is used much differently than any other shotgun in the hunting and sporting world. We aim turkey guns at a relatively small target (neck/head) much like a rifle and ALL turkey combo's (gun, choke, load) in 12 or 20 ga suffer from inaccuracy, pattern patchyness and poor pattern repeatability at distances beyond 35 yards so why do we spend so much time and money trying to find that magical 40 yd combo???? Okay, maybe it's number 4!