Why do shot shells come in whole sizes 4,5,6,7,8,9 Plus 7-1/2 ? What is so special about 7-1/2? that it is needed in addition to 7 and 8? Why not 6-1/2 and 8-1/2?7-1/2 predates steel shot by several generations, so not that.

[Gmuleman]

Why do shot shells come in whole sizes 4,5,6,7,8,9 Plus 7-1/2 ? What is so special about 7-1/2? that it is needed in addition to 7 and 8? Why not 6-1/2 and 8-1/2? 7-1/2 predates steel shot by several generations, so not that.

[JM]

The 1/2 is just an extra measurement(extra decimal) of the shot size. 7 1/2 shot has a 0.095 inch diameter. 8 shot has a diameter of 0.09 inches. 8 1/2 shot has a measurement of 0.085 inches.
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Edit: Not sure the top of my answer is what you were asking, so he's another answer. Take the shot out of a 7, a 7 1/2 , and an 8. Small difference, but you can tell which is which. Simple math is that the smaller the diameter of the shot the more that will fit into one shell. People felt like there was enough of a difference between a 7 and an 8 that something in-between was useful. Once you start getting smaller than an 8 1/2 the shot is so small that the extra 0.005" wouldn't really change anything. Once you start using bigger than 7 shot the 0.005" isn't really necessary because shot pattern etc. becomes less of an issue.

[huntfishtrap]

The 1/2 is just an extra measurement(extra decimal) of the shot size. 7 1/2 shot has a 0.095 inch diameter. 8 shot has a diameter of 0.09 inches. 8 1/2 shot has a measurement of 0.085 inches.
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Edit: Not sure the top of my answer is what you were asking, so he's another answer. Take the shot out of a 7, a 7 1/2 , and an 8. Small difference, but you can tell which is which. Simple math is that the smaller the diameter of the shot the more that will fit into one shell. People felt like there was enough of a difference between a 7 and an 8 that something in-between was useful. Once you start getting smaller than an 8 1/2 the shot is so small that the extra 0.005" wouldn't really change anything. Once you start using bigger than 7 shot the 0.005" isn't really necessary because shot pattern etc. becomes less of an issue.

I was curious about this too. What I wonder is - why is 7 1/2 so much more popular than 7? You very rarely see 7 shot, apart from Hevi-Shot turkey loads. I admit, I'm not sure 7 1/2 is really necessary, since I usually use 8s for target shooting and 6s or bigger for hunting.

[Okwaho]

I don't know, but I wouldn't be surprised if it originally had something to do with competitive trap and skeet shooting. As with any sports, those who are really into it will get right down to the nitty-gritty (hand a billiards player a cue-stick one ounce too big or small and he'll hand it right back). As for a bird-hunter's point of view: I use 7.5s myself for ruffed grouse because I just feel like 8s are a bit too small. I'd use 7s, no problem, but I've never seen them in a store.

[JM]

The 1/2 is just an extra measurement(extra decimal) of the shot size. 7 1/2 shot has a 0.095 inch diameter. 8 shot has a diameter of 0.09 inches. 8 1/2 shot has a measurement of 0.085 inches.
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Edit: Not sure the top of my answer is what you were asking, so he's another answer. Take the shot out of a 7, a 7 1/2 , and an 8. Small difference, but you can tell which is which. Simple math is that the smaller the diameter of the shot the more that will fit into one shell. People felt like there was enough of a difference between a 7 and an 8 that something in-between was useful. Once you start getting smaller than an 8 1/2 the shot is so small that the extra 0.005" wouldn't really change anything. Once you start using bigger than 7 shot the 0.005" isn't really necessary because shot pattern etc. becomes less of an issue.

According to an old family friend, people did not think that 8 shot flew very well, so they came up with the 7.5.

[woodcockpro]

I don't know, but I sure like 7 1/2 for woodcock hunting, it does the best out of my .410 for shorter ranges.

[charlie elk]

7.5 are high brass, this is an old term meaning they have more gun powder. They were developed for early season close flushing pheasants. 7.5 are commonly used in areas where grouse, partridge and quail may present an opportunity.
#8 and up are low brass so they have less terminal power by design. I do not use these for hunting. So I suppose you could say 7.5 is the dividing line between hunting and target loads.
7's are a more recent development to accommodate nontoxic shot.

[huntfishtrap]

7.5 are high brass, this is an old term meaning they have more gun powder. They were developed for early season close flushing pheasants. 7.5 are commonly used in areas where grouse, partridge and quail may present an opportunity.
#8 and up are low brass so they have less terminal power by design. I do not use these for hunting. So I suppose you could say 7.5 is the dividing line between hunting and target loads.
7's are a more recent development to accommodate nontoxic shot.

I personally would not use 7.5s for pheasants. Just a little too light for me.

[jhjimbo]

7.5 are high brass, this is an old term meaning they have more gun powder. They were developed for early season close flushing pheasants. 7.5 are commonly used in areas where grouse, partridge and quail may present an opportunity.
#8 and up are low brass so they have less terminal power by design. I do not use these for hunting. So I suppose you could say 7.5 is the dividing line between hunting and target loads.
7's are a more recent development to accommodate nontoxic shot.

I would use 5 or 6 for Pheasant.

[jhjimbo]

The 1/2 is just an extra measurement(extra decimal) of the shot size. 7 1/2 shot has a 0.095 inch diameter. 8 shot has a diameter of 0.09 inches. 8 1/2 shot has a measurement of 0.085 inches.
-
-
Edit: Not sure the top of my answer is what you were asking, so he's another answer. Take the shot out of a 7, a 7 1/2 , and an 8. Small difference, but you can tell which is which. Simple math is that the smaller the diameter of the shot the more that will fit into one shell. People felt like there was enough of a difference between a 7 and an 8 that something in-between was useful. Once you start getting smaller than an 8 1/2 the shot is so small that the extra 0.005" wouldn't really change anything. Once you start using bigger than 7 shot the 0.005" isn't really necessary because shot pattern etc. becomes less of an issue.

I never knew this.

[charlie elk]

7.5 are high brass, this is an old term meaning they have more gun powder. They were developed for early season close flushing pheasants. 7.5 are commonly used in areas where grouse, partridge and quail may present an opportunity.
#8 and up are low brass so they have less terminal power by design. I do not use these for hunting. So I suppose you could say 7.5 is the dividing line between hunting and target loads.
7's are a more recent development to accommodate nontoxic shot.

Back in the days gone by shotguns had fixed choke barrels many of which were very marginal at keeping patterns tight, that's why they were referred to as scatter-guns. Plus the wad if you could call it that by today's standards was a piece of cardboard separating the shot from the powder. 7.5 provided more pellets for a denser pattern. We got closer to our game than hunters do now.

[huntfishtrap]

7.5 are high brass, this is an old term meaning they have more gun powder. They were developed for early season close flushing pheasants. 7.5 are commonly used in areas where grouse, partridge and quail may present an opportunity.
#8 and up are low brass so they have less terminal power by design. I do not use these for hunting. So I suppose you could say 7.5 is the dividing line between hunting and target loads.
7's are a more recent development to accommodate nontoxic shot.

So charlie, if I'm reading your comment right, you're saying that you are from days gone by?

[charlie elk]

7.5 are high brass, this is an old term meaning they have more gun powder. They were developed for early season close flushing pheasants. 7.5 are commonly used in areas where grouse, partridge and quail may present an opportunity.
#8 and up are low brass so they have less terminal power by design. I do not use these for hunting. So I suppose you could say 7.5 is the dividing line between hunting and target loads.
7's are a more recent development to accommodate nontoxic shot.

Yep, proudly.

[John B. Snow]

The answer is pretty simple. It's just another option hunting and/or target use. There's nothing special or magical about 7-1/2s, but, to Charlie Elk's point, it sort of allows a person to split the difference between traditional target and hunting loads.
I guess if I were forced to make the case for 7-1/2s, it is a bit of a "do-it-all" shot size. You can use them on the really light birds (or clays) and they have enough ummph to take down pheasant and grouse--though I'll be honest, it wouldn't be my first choice for either of those birds.