I am wondering if the spread of a shotshell is logarithmic? The reason I ask is I have a pattern board that only holds a 36"x36" piece of paper so I plan on using a 30" circle at 30 yards. Would that be equivalent to a 40" circle at 40 yards, practically and/or theoretically? Could I make the same assumptions about the choke size?

http://www.claytargettesting.com/index.html

Pattern the gun is the best way. If the shot string is above the speed of sound then the shot is going against a near vertical "wall" of compressed air. The shot string will close and slow very rapidly. Even the fastest load is subsonic somewhere around 20 yards. Then the normal flat plate drag laws associated with subsonic flight take over. That is usually an expansion of one inch per yard of travel. It's extremely hard to calculate because the shot coming from the barrel is very irregular and will make for a large and irregular bow wave. The speed of sound varies with the temperature so the the time spent for the shot to remain supersonic can vary. You are dealing with an irregular vehicle (shot group) and a quick change of temperature change from shotgun barrel to ambient traveling in the trans sonic speed range. Given the variables patterning the gun is the best way to get the information you want.

Sorry but I only understand about half of what you have written regarding supersonic and subsonic and the impact each has on the pattern. When you wrote 'pattern the gun is the best way', are you suggesting to test it at logarithmic distances i.e.. 10, 20, 40 yards? I'm not sure what impact shot string has on the pattern?

All about drag when a projectile comes back through the sound barrier and passes through its own shock wave in a way. More a problem for long range target shooters. A 7.62mm. military bullet comes back through the sound barrier somewhere around the 900 to 1,000 yard mark and gets very upset and unstable before it settles down again. I've put them all in the black at 900 yards and then had a job finding the target when dropping back to 1,000. Shotgun patterns are 3 dimentional and as Pooch says, each pellet will be a slightly different shape and even travelling at a slightly different speed even after a few yards so it is very difficult to predict mathematically. Interesting question none the less. Lagopus.....

Forget logs. Just pattern the gun. Experiment with the shot load you are most likely to use and compare, an analog solution, but it is not logarithmic.

Tamid,

I can't answer that question for you, but I can tell you that in my experience you will learn a lot more from patterning at distances shorter than 40 yards than you will from not patterning at all. You can learn a lot at 30 yards and less.

SRH

Stan is right. A lot of bird shooting is less than 40 yards so I think you learn a lot by patterning at distances that you actually shoot.

Stan is right. Pattern the gun at ranges you expect to shoot. That will tell you if you are going to succeed!

Tamid, this s a very good question. Unfortunately, the answer is complex. Fortunately, Dr. A C. Jones addressed this question in his book "Sporting Shotgun Performance." You can get an intuitive idea of performance/pattern comparisons by "eye-ball integration" of patterns. However, it would be more worthwhile to use the shotgun insights program to generate statistically valid data.

Briefly, patterns have a Rayleigh distribution (you can use a normal distribution with only a small loss of accuracy) from muzzle until the shot hits the ground. That said, pattern can be calculated up and down the range once it is established. The fly in the ointment is that the diameter of the effective area of the pattern blooms for some distance (influenced by choke) and then withers as the number of pellets becomes insufficient to cover the ever expanding pattern area.

The expansion is not a log function. The following estimate is not too far off: 10 yds to 20 yds - double, 20 yds to 30 yds -double, 30 yds to 40 yds - 1.5X, and 40 yds to 50 yds - 1.5X. Keep in mind that this does not give you effective diameter, rather linear area.

Hope that helps some.

DDA

I pattern game guns at 30 yards these days. When they took lead away from me I had to stop pass shooting ducks. Well I shot more crows that ducks some years. Still my days of shooting a large number of birds at 40 plus yards is over. I find that most of my shooting is between 25 and 35 yards. So what patterns well at 30 seems to work well for me at the rest.

Consider erecting a grease plate, as opposed to only shooting paper. I have shot paper, for patterning, for some 30 years, but only recently built a grease plate. It is a couple miles from home on another piece of property I own, but I'm over there a lot. I've found that I shoot many more patterns with the grease plate than I did with paper because it is always ready. Just roll the paint/oil mixture to erase the last pattern and it's ready to go. The only costs I incurred was the piece of 4' x 4'x 3/16" steel plate and two treated 4" x 4" posts. I had enough scrap, treated 2" x 8"s, to build the framework backing for the plate. I take pics of the patterns if I want to save them, and download onto my computer. Easy, peasy.

I can shoot it as far back as 100+ yds., if I want to. Want to get your feelings hurt? Take your favorite bird gun that has a modified choke in one barrel and pattern it at 60 yds. with a 1 1/8 oz. load. Then look at the number of holes a bird could easily fly through. It's almost enough to make you lose confidence in shooting clay birds at that distance. I shoot a lot of targets on sporting clays courses at 50 - 70 yds., and I can tell you that I am now amazed when I can break 4 long birds straight on a station.

As Tim Conway used to say on the Carol Burnett Show .........very, very in-te-rest-ing.

SRH

I have a couple of "standard" loads for several of my SxS guns all reloaded duplicates of factory shells. B&P & RST mostly. Patterning them I use a 12 inch circle drawn on construction paper. Pattern both barrels at expected distances. Spreaders 10 20 and 30 yards. 7/8 loads 20 30 & 40 sometimes add a 50 yard pattern.

It tells me 30 is too far for my spreader loads and 50 is to far 7/8 oz. Other distances gives me confidence that gun/load will break a clay target if I am on the bird. Don't think I would gain much confidence interpolation off a single distance.

Using a larger paper & circle may be better for load development. All I am doing is gaining confidence in the combination and not worried about percentages compared to published standards

Stan I have used our clubs steel plate at longer distances and like you found its a confidence looser.

Boats

Tamid, you can indeed "guesstimate" what your pattern will be at longer ranges by shooting closer patterns. Works relatively well for everything except guns with tight chokes (F and maybe IM), which don't open the same way the more open chokes do. The late Bob Brister's wife, when Brister was working on his book and attempting to explain that fact, told him all he needed to say was that IC goes to hell gradually while full does so all at once.

Anyhow, here's the ballpark formula for guns choked no tighter than Mod: For every 5 yards of distance you add, your pattern will drop 10%. Cylinder, which should throw about 70% at 25 yards, drops to 60% at 30 yards, 50% at 35 yards, 40% at 40 yards. Those are only ballpark numbers and will, of course, depend on the specific load you're shooting.

Where I lived in Iowa for almost 20 years, I had a patterning setup that limited me to 30 yard shots. Always figured I could get a pretty good idea how things would look at 40 yards by shooting at 30 and doing the math. And in my case, I was much more interested in how my guns patterned at 30 yards (or even closer) than I was at 40 yards anyhow--not being a waterfowl hunter, and seldom taking 40 yard shots at upland birds.

For a large number if years I have observed the pattern tests run in the American Rifleman when they tested a new model gun. I have thus observed a lot more of these than actually doing tests of my own. They have consistently used a pattern which contained a 30" circle & an inner circle of 21" (49% of the 30") & this divided into 4 quarters. All patterning has been done at the traditional 40 yds. The one thing I have noted is the tighter chokes producing patterns of around 70% typically have a higher concentration of that pattern in the inner circle. regardless of choke it is always more than half.
On a well centered hit the tight choke will give much greater range for adequate killing power but is of course surrounded by a large area with insufficient density of shot.
As I view it this would be the exact opposite of what Brister's wife said. The open chokes will give you a wider spread of adequate density at shorter ranges but will play out much closer to the same range than will the full. Even a IC choke will maintain density further on a centered hit than on the fringes but is not as drastically so as the full.

Shot Pattern Spread from Field and Stream Sept 1964. I do not have the original article but assume the shells were Winchester/Western Mark 5 with the polyethylene shot collar introduced in 1961. Modern loads are very likely better.

…………………………………………YARDS………………………….
.....…….....10…… 15……20……25……30……35……40
CHOKE
Full…………. 9……..12……16……21……26……33……40 inches

Mod……..……12…….16……20……26……32……38……46 inches

Imp Cyl……..15…….20……26……32……38……44……51 inches

Cylinder…… 19……26……32……38……44……51……57 inches

Tamid -

I pity you trying to make sense of near senseless ramblings. Unless a barrel has been modified in some way, the original choke markings will be as indicative as anything of killing effectiveness if you use standard ammo. You can pattern all you like at any distance that rings your bell and the most important thing that patterning will tell you is the POI of that gun with you shooting it. Trying to make a great conclusion out of shotgun patterns is a waste of time. Do what Mr. Winston says in the link I provided above and then spend some quality time shooting
So here's the essentials as they work for me:
IC for close targets - my IC will kill out to about 30yds but closer is better. I used a 0.012/#3 choke in a Perazzi for the first barrel at pigeons and that was 30+yds solid kills at the box
M for intermediate targets - harder to kill closer targets and OK for the 1st barrel at pigeons but prolly not necessary
F Again in the pigeon ring since I KNOW what those distances are, a F will kill at the fence at +/-60yds.

In my experience the choke markings on any Italian gun tell me all I need to know about how that gun will kill. I have no reason to suspect that the original marking/choke on any reasonable quality gun would be any different

besta luck

have another day
Dr.WtS

One other thing to remember. I have an engineering background and spent a life time dealing with items in the trans sonic speed range. This can drive a man to drink. I pattern probably too much. I had a friend that I used to hunt ducks, geese and cranes with. We both shot 12ga SBEs. I used to tell him not to used 3 1/2 Ts in his SBE because the patterns would fall apart. He nodded his head and went ahead shooting the Ts. He consistently out shot me. It goes back to an old English axiom: A poor pattern on target kills better then a good pattern off.

What we have here is an unruly projectile flying at trans sonic speeds fired by a human being. This gets into the math of chaos realm and science is not yet ready to crack a problem with this many variables. Pattern, shoot what works for you, do what comes natural and don't waste time thinking about it.

From my personal experience I am more often over choked than under choked but I do limit my ranges whenever possible. I rarely take 40 plus yard shots at game unless it is a followup shot on a bird already hit closer. Now clay targets are often shot at longer ranges but as they say a wounded clay target is scored dead and does not fly off to die later. Some of my favorite Sporting Clay courses seem to think a falling teal needs to be at 50 yards to be any challenge. Add in wind and low temperatures and every hit is an achievement.

Patterning guns can play with your mind when your favorite load looks no better than five others. Worse never pattern your .410 because it will give you doubts about the .410 ever hitting birds at all. I've seen loads which consistently smoked clay targets which when pattern on paper did not look at all impressive. And if you pour out your .410 shot charge into your hand you will think is that all there is. Wow it is a little gun.

I find POI is more important to my shooting most of the time than a slightly tighter choke selection. A great pattern does not do much if 50-75% is off target to start with because your POI is off. So while you are patterning those loads do not forget to check your POI at some point. And extra layers of clothing, shooting from a sitting position or from a layout blind does change things.

I pity you, thinking that everyone but you is a (near) nonsensical idiot. But, I guess ,as always, it's up to the OP to determine which answers seem reasonable and which do not. Probably makes it much easier on him when the California Sage comes along and puts everyone else in their place, tho'.

SRH

Miller, here are a few quotes from Brister's chapter "Choosing Chokes and Loads", including the following, which is the very first sentence in the chapter: "Full choke is a demanding mistress; improved cylinder a forgiving friend."

"However said, the significance is that at the distances at which much game is killed, between 20 and 38 yards, the IC is at its best, offering adequate killing density but at the same time a nice, broad spread to give the shooter more margin for error."

Re full, Brister gives its "reign of superiority" as between 40-50 yards. But also notes that aiming errors are magnified with range; that pellets are losing more speed (hence, more energy); and string becomes more of an issue. He points out that full is less efficient at 55 yards than is IC at 40. Since you don't really need full until you get to 40 (or more), it actually has a rather short useful range--although if you're shooting regularly at that range, then full is clearly what you need. But it handicaps you under 40 yards, when you don't need it . . . and then runs out of steam fairly quickly.

You know me - always ready to help out. Good to be appreciated.
thanks


have another day
Dr.WtS

I should offer more usable advice then launching into a diatribe about the mathematics of chaos, sorry. The expansion of the shot field is pretty linear over the distance we will be shooting. Shooting a large number of patterns is time consuming and hard on the shoulder. Find the data where someone else has done the patterning and use that data.

I think, in a nutshell, what pooch was trying to say is.....get larger paper, and shoot at it from 40 yards.....lol.

That would be a more accurate patterning technique.

You local newspaper will be more then happy to give you their roll ends off their paper rolls to get them out of the way. They are big enough to get the whole pattern on the paper.

Home depot sells 48" rolls of heavy duty brown paper for cheap. If a pellet does not penetrate it at 40 yards....it's no good to a hunter anyway.

Also a good idea pooch....if you can find a local news paper these days.

I bought the Home Depot brown paper but up here it only comes in 36". And as for newspaper. They are almost out of business if they haven't succumbed yet.

Pooch, now I'm perplexed. How will someone else's patterning tell me anything about how my gun will pattern the same loads? And if you hand load, like I do with black powder, there are few who load the same way with the same components.

If you are using black powder then the flight path performance is pretty simple as only a small part, if any of your shot will be supersonic. Just copy somebody that has shot the same load with the same muzzle velocity and your pattern work is already done. Black or nitro makes little difference. If you are following the old rule of 96 the expansion of shot and the decay of energy is what we call straight line. Shoot a pattern at 30 yds measure it, then measure your barrel diameter the distances between those two points will be proportional or close enough to proportional and will depend more on the wind and shooting consistency.