Why Shotgun Patterns Change Even With the Same Gauge

You could spend all your time reading choke charts and shell specs, and still be shocked the first time you put a shotgun on paper. You could have 2 identical 12-gauge setups that look pretty much the same on paper that still leave totally different patterns at the same distance.

Why? The reason is actually simple. ’12 gauge’ doesn’t say a lot. 

People think it does, but it really doesn’t.

The gauge size tells you the bore size. This information alone won’t tell you much about how the shot is going to behave once it’s out of the barrel. Changing the choice can make the pattern much tighter. If you change the shell, you introduce more changes in how it behaves.

If you really want to know what a particular setup does, the paper target will tell you more than the box.

The Same 12 Gauge Can Put Out Very Different Patterns on Paper

A 12 gauge is a 12 gauge, right? The spread should be pretty consistent because nothing else makes sense.

As it turns out, though, that’s not really the case. 

A good example here is the choke test with a Winchester 2 ¾ -inch #8 lead shell.

What happened is that when fired with a cylinder choke, the shell pattern was approx. 21 inches wide at the 30 yard mark. Though a modified choke, the same test measured a 10-inch-wide spread.

If you research ‘how much shot spreads every few yards’ (or something similar to that) you’ll get a rough idea of what you might expect – a ballpark figure – but you won’t be able to exactly know what’ll happen.

Also, you can’t look at just the width. 

A pattern can look relatively wide but still have an even center. Another one could be more or less the same size and have obvious holes where hardly any pellets have landed. 

Then when you’re analyzing the target, you’re not looking just at how far the pellets have spread, but also at how evenly they got there.

The shell you’re using is also a highly determining factor here.

If you go online and look up some 12 gauge ammo for sale (or similar) options, next to the price point, you’ll also see the specs (e.g., shot size, payload, velocity, shell design, material, choke/barrel differences, etc.), which can point you towards how the shell will behave.

Overall, all ’12 gauge’ gives you is the basic category. If you want to know what the target’ll look like, you’ll have to dig deeper.

Things That Can Change a Shotgun Pattern

If you’d stop looking at the gauge like it’s going to tell you the whole story, you’d be able to see that things are actually more interesting than you think they are. 

Let’s see what affects a shotgun pattern.

Two Shotguns of the Same Model Can Still Pattern Differently

You could have 2 shotguns with the same name on the side, and they still don’t necessarily have to shoot exactly alike. Even the smallest differences inside a barrel can have a higher effect than what you’d expect.

For instance, a tighter bore will force out the pellets through the barrel differently than a wider one.

The Choke

The choke determines what happens right before the shot leaves the barrel, so of course it’s going to affect the pattern. Naturally.

A tighter choke will (usually) keep the pellets together longer, and a more open choke will let them start spreading sooner.

Because of this ‘obvious’ factor, users have the tendency to expect too much from what’s on the label. ‘Modified’ is a tricky term because it doesn’t mean that every shotgun will have the same size pattern at 30 yards. ‘Cylinder’ also won’t guarantee spread. also doesn’t come with a guaranteed spread. 

These label names will tell you more about how much constriction you’re dealing with rather than telling you what outcome to expect.

What’s Inside the Shell?

From the outside, 2 shells can look 100% the same. 

But that doesn’t (necessarily) mean that what’s in them isn’t doing different things. The size of the pellet changes how many pellets you have to work with, and payload weight changes how much shot is packed into the shell.

Pellet size > pellet count. A 5-meter shot test study has shown that #9 lead shots produce approx. a 1.7 times larger (70% increased area of effect) pattern than a #0 lead shot. – Journal of Forensic Sciences

The pellets themselves are a determining factor here – softer pellets can suffer flattening/denting during the firing action. And as soon as the pellets aren’t perfectly round anymore, their flight trajectory becomes more erratic/unpredictable.

Conclusion

Shotgun shot patterns are highly fascinating (even if you’re familiar with them). This probably has much to do with how the gauge is only one small part of how it all works. You also have choke, dimensions of the barrel, size of the pellet, wad design, payload, and distance that can change what happens after the shot leaves the muzzle.

The key takeaway from this entire article is that what’s on the label of a shotgun won’t dictate how it behaves in the real-world.