doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Pattern density between gauges

That's the best title I could come up with, but I'm not sure it describes my question. Heck, I'm not even sure I can express it well enough to communicate, but here goes.

I am of the belief that sufficient pattern DENSITY, at a sufficient velocity and with sufficient pellet mass, is what kills birds and breaks targets. In other words, if the velocity and the mass of the pellet(s) is enough (retained energy), density in the pattern is what puts the shot on the bird. Greater density, greater number of hits on target, provided the target is within the pattern area.

If that is so, then the same pattern density delivered from a .410 will kill and break a target equal to a 12 ga. Don't get riled up yet, I'm going to qualify that. If the same pellet size is used, at the same velocity, and the pattern density is the same, the bird will not know if it has been hit by a 12 or a .410.

Now, as to pattern density. It is absolutely truthful to say the above can be done, and is done. But, at what cost? Pattern size. The density of a pattern fired from a 1 1/8 oz. load can equal the density of one from a 11/16 oz. load at the same distance, if greater choke constriction is used in the .410 to accomplish this. This, again, reduces the overall diameter of the 11/16 oz. pattern and makes putting that pattern on target more difficult.

So, if I haven't been tried and convicted of heresy yet, how can this be calculated? Have charts ever been published that show, for example, what diameter the pattern from a 11/16 oz. load of #8s would have to be to equal the density in a 30" pattern from a 1 1/8 oz. load of #8s (100% patterns)? I'm not much at math, admittedly, but I know many of you could quickly calculate this. I also may not have done a very good job of communicating this, and please feel free to cover any variables I may have missed. But, hopefully, charts exist somewhere showing these comparisons.

SRH

Stan, IMO, uou have communicated a good question very accurately! The answer is a qualified "Yes." I say qualified because the calculation is not simple, not at all. The reason is that patterns never have a uniform distribution of shot. The pattern always exhibits a Rayleigh distribution; the same distribution as governs bomb patterns, artillery fire, and rifle fire. It is fair to think of a shot pattern as a "bunch of rifle bullets all fired at the same time." Rifle fire would make a smaller pattern, but the distribution within the pattern would be the same 'ole Rayleigh distribution.

We can make a passable SWAG (note that this is not the real statistical calculation, but it will do for illustration) by saying that the .410 will have about 11/18 (11/16 / (18/16)), that is 61%, of the effective area of the 12 bore. Lets say, for grins, that at the distance and with desired choke, the 12 has a 24" effective diameter; that is 452 square inches. The .410, then, has 61% of 452 = 276 square inches. The radius for 276 is the square root of 88, which is 9.4 inches. So, the diameter is 2 X 9.4 = 18.8". Note that your aiming error with the .410 must be not worse than 78% of aiming error with the 12 bore. As you can see, the situation for the .410 is not as bad as is often presumed.

Hope that helps. BTW, post back if you need more detail with the math.

DDA

Stan, in the calculating of patterns whether it is a .410 or 10 gauge, the percentage is achieved by how many pellets are in a 30" circle at 40 yards. In order to get the percentage, the amount in the circle is then taken by how many pellets are in that load to begin with, whether it is #9's or #4's.
Both the .410 and 10 gauge can have the same percentage.

"If that is so, then the same pattern density delivered from a .410 will kill and break a target equal to a 12 ga. Don't get riled up yet, I'm going to qualify that. If the same pellet size is used, at the same velocity, and the pattern density is the same, the bird will not know if it has been hit by a 12 or a .410."

I think everyone will agree with that. It is all about putting the shot where it counts.
I did you did a good job explaining your point.

Stan,

in theory this is absolutely correct.

The practical application, however, has its limits. One could kill game with a .410 as far as with a 12, if one could get a .410 to pattern as densely as the 12 (at the expense of a smaller killing circle). The "if" is a big question. I have known people who tried to achieve this pattern density with 20s and .410s, claiming that this would make their shooting more sporting. None of the attempts were successful. Besides, all experiments with extra long shotgun ammo known to me suggest that the tighter the pattern is, that is, the less space there is between individual pellets, and the more bulletlike is the pattern in behavior, the less predictable is the flight. One is bound to get problems with POI to POA consistency, for instance.

So, while the theoretical reasoning is flawless, I doubt that in real life anyone can kills with a .410 as far as with a 12 bore.

There is also the fact that patterns deteriorate at an exponential rate and though their 'silhouettes' may be similar in shape they will not be in density at any significant similar distance from the muzzle. Speaking here of differing charge weights of same size shot. Nonetheless, there should be a point [distance from the muzzle] that pattern effectiveness is similar from one gauge to another though they will be dif from one to another in distance. That is the comparitive 'sweet spot' or equality point that you are referring to.

I do not think it is any more easily arrived at mathematically than a pattern can be forecast. That random behaviour within parameters [observed limits?] is always going to remain proximate, rather than exact.

The likely reason there is no such chart existent is that the nature of the problem is not wholly linear. Lest I have confused anyone, I do not argue your thinking at all, Stan. However, aside from some extensive empirical pattern testing with the specific loads & guns you might wish to use, knowing the exact range where that 'sameness' exists for both guns & loads would at best be a SWAG. And then what are the odds of encountering game or target at the exact desired range?!

It is much easier to simply limit shots taken with <3/4oz. payloads to inside 30 yards & use shot of sufficient size for the intended target. 3/4 oz. payloads [not only in 28's, but 20's & 12's too] can & do put mourning dove & other upland birds in the bag & break bunker targets at ranges of 35yards + with what would seem disportionate regularity. Brister was quite intrigued with that observation in regards to the 28 ga. & went to some length to find out why it was the case & wrote a book on the subject. Was it difinitive or absolute? Yes & no. It did shed a lot of then new & interesting light on the quest for an answer. He did not, that I recall, ever ask nor speak to your observation.

I'd call it an observation more than a question and a valid one, but I have no expectation of seeing an equivalence chart of assorted gauges vs. range anytime soon, though I guess someone might play with it on an X/Y axis using a linear regression from a lot of testing & data points & come up with a rule of thumb kinda thing. Not sure what one would do with it if it existed.

No doubt, you could likely publish your findings in an article of interest as Sherman Bell has done. I dunno whether I'd call it a potential hornet's nest, a pinata or a can o' worms;-);-)The validity of your observation is real enough, however the proof in any absolute graphic is problematic.

Best, tw

Good points, and I do recognize the problem with shot stringing and pattern degeneration in the .410 especially, due to a higher percentage of the pellets being deformed due to setback, etc.

My idea is not to try and make the .410 equal to the 12, or any gauge in between, but to have a means to say, within reason, "Okay, I know how far I can dependably kill a dove with my 20 ga., 7/8 oz. of 7 1/2s and .020" choke. At what range do I need to turn down a shot with my .410, given that it has .032" choke and I'm using 11/16 oz. of the same 7 1/2s. Again, I'm asking about pattern density only, and I know how hard it is to keep shootability, shot stringing, moon phases and the constant shifting of magnetic north out of the discussion. And I am not belittling any of those real or perceived influences, just trying to get to the actual numbers.

You're right that each gun is different, and is a rule to itself. But, that doesn't keep every gun related outfit that comes along from publishing their own version of the "choke chart", showing what the constriction of each commonly referred to choke is actually dimensioned. We saw that in a recent thread. Is this any more difficult to determine than that?

Miller, I know you could tell me what the method is to determine this. Couldn't one simply determine the number of shot in the payload and use the square inch area of the pattern diameters to get a comparable density? Help me determine the formula(e) to use and I'll make the blasted chart myself!

SRH

"IF" shot distribution was uniform throughout the pattern this would be very simple to calculate. Given the same choke percentage the 1 1/8oz load would have the same density as the 11/16oz one at 28% greater range. To have equal density the 11/16oz would have to make a 100% pattern at the range the 1 1/8oz made a 61% pattern.
It is of course not quite this simple as R'Man pointed out. There is even a bit of evidence that the pattern from a smaller bore might have more of a tendency to central thickening than the larger bore. "IF" this be true then the 100% .410 with 11/16oz could have a slightly greater range than the 61% 1 1/8oz on a perfectly centered shot, but the larger gun would have a better fringe area.

Another fly in this admittedly interesting jar of ointment: you can't go by "book" figures to obtain accurate pellet count in a given load. Before you base your assumptions on 350 7 1/2's per ounce, you need to check each individual brand of shell (even from the same shotshell maker) to see how many pellets you have. The "book value", I've found, is just a rough average. I've found 6's--talking supposedly American 6 here, not the smaller British 6--that count out around 200/oz; others close to 250. On either end, that's a 10% deviation from the "book" number of 225. And really bad news if you're comparing the two extremes. Likewise, I recently counted Rem Gun Club and STS 20ga 7/8 oz 8's and found a significant difference there as well.

Obviously, if you're going to compute density accurately, you can't just assume that the load in question contains the number of pellets it should contain based on "book" figures.

That's the numbers I'm talking about, Miller. Thanks, now how'd you get them?

SRH

Stan,
All said and done...and as others have alluded, given all the variables of ammunition, forcing cones, choke cones and whatever else I didn't think of, I think empirical exploration (pattern testing) along with a rough SWAG, is going to accomplish what you want in a much more expedient manner and with greater accuracy. From that data, you could build a chart.

I've had some 3/4 oz and 11/16 oz .410 loads that had great pattern distributions and some that didn't in various guns for various reasons, most of which I never figured out, but only speculated. As I'm sure you're aware, the .410 is a fairly fickle firearm. I love 'em.