As per a John Barsness article - he was very specific about the benefits of # 7 shot in 28 gauge for grouse and pheasant - at least in Montana. The commotion that a guy goes through to get a limit of what - 3 birds, now-a-days???
As gun writers go, John Barsness is better than average. However, I will very specifically say there is no benefit to either a 28 gauge with #7 shot for pheasant in Montana - unless perhaps there's a deadline approaching and you're a gun writer.
My wife and I may not shoot as many cacklebirds in Montana over our Griffs every year as Barsness - but if we don't, it's pretty close. And not in one corner of Montana at one time of the year, but all over Montana during all parts of the season. There's quite a range of hunting conditions for roosters and sharpies in Montana:
If he's hunting somewhere, with a good pointer, and he's putting sharpies and cacklebirds up right at his dog's nose, then a 28 gauge and #7 is adequate. Adequate - not beneficial. There's a difference. A few ounces lighter than a similar 20 gauge if you're getting too long in the tooth to manage carrying the extra ounces in a bigger bore shotgun. Beyond that, it's a handicap and in my mind unethical for the birds.
I bought an Aya 28 gauge from Lee Strait about 1980 because it was the prettiest shotgun I'd ever seen and felt like a wand in my hands. I was a regular and fairly decent trap and skeet shooter at the time, so I wasn't a complete klutz with a shotgun. After a couple of hunting seasons, the Aya moved down the road to another home; far too many cripples for me to keep hunting with it. For hunting quail and Huns it was the bomb, but my hunting for those birds wasn't often enough for the Aya to remain in the gun safe when a replacement over/under with interchangeable 12 and 20 gauge barrels became available.
The maximum 28 ga. shot charge at that time as I recall reloading was 3/4 oz. of whatever flavour of shot you chose; in my case #6. Stack that in a tall, narrow 28 gauge hull, and the result is that even if you've spent hours shooting at the patterning board, sorting your reloads out to find what works best, flying through the air you have a long, strung out pattern in comparison to a 20 gauge for example. Definitely not optimal for reliably crumpling roosters or sharpies other than for the guys who can center the bird with the pattern every time.
Pheasant season in Montana starts in October; the season ends at the end of the year. The birds are already starting to feather out for winter by October, and pretty much in full plumage by November and December. And unless you've got a secret sauce CRP location, a land owner who allows only you and a few others, etc. the remaining birds as the year progresses get increasingly wily. Meaning they don't wait until you step on their tails before flushing. Meaning you're getting your opportunities further and further out, closer to the edge of the range where a 3/4 oz. pattern out of any gauge is no longer effective. And at ranges where the allegedly beneficial #7 shot in a light shot load is not carrying enough energy for the number of shot that arrives at the bird, versus a heavier charge of #7 and where switching to #6 gains energy, but now you're down to even fewer pellets arriving at the bird.
Other than for a specialist or in optimal conditions, a 28 gauge with #7 shot is a lose/lose proposition for pheasants and sharpies in Montana. Despite a Montana based gun writer saying otherwise. It just gets worse if you want to hunt one of the Heritage People reservations or federal wildlife/habitat reserves in Montana that compel the use of steel shot in a 28 gauge (which is irrelevant to your question about sorting #7 lead shot with other mixed in, of course).
My wife and I have been hunting pheasants in Montana with Griffs since we met hunting birds 25 years ago while she was teaching at the University of Idaho. What we have settled on as reliable cacklebird crumplers is 1 oz. of #7 first off out of the bottom barrel with IC choke, followed by 1 1/8 of #6 out of the top barrel with a modified for misses, or following birds. That's opening season with unwary birds. After that, it becomes 1 1/8 of #6 using modified, followed by 1 1/4 oz. of #5 with full choke. For wary/late season birds, even with the Griffs, the birds are getting up at 25 yards or so, and by the time your gun is mounted, they're out there.
Those combinations over the years have delivered the balance of being reliable bird crumplers with few cripples without tearing up the birds you center, resulting in less than optimal pheasant for supper that night. I will also suggest fairly confidently that you will find it far easier to find good pattern performance with a lot less experimenting and tuning the bigger the gauge. I.e. 12 is the easiest, .410 is the worst at the other end of the scale; number of pellets and shot string dimensions are what is at play.
None of that has much to do with sorting other sizes from #7 - a very good shot size that can be hard to source for reloading. But unless you have a plan that will put you on top of roosters and sharpies when they flush, 3/4 oz. of #7 out of any gauge is not going to be either beneficial nor optimal. Unless you're a shotgun sniper that centers them all, you're going to have too many birds that you just hit with the fringe of the pattern, cripples lost to die out in the grass that you would have put in the bag with 1 oz. or 1 1/8 oz. with the same fringe hits.
Anyways, I'm not a professional gun writer like John Barnsness, but I have shot a fair number of cacklebirds and sharpies in Montana and elsewhere over the last 40 years, and that's my observations and opinion based on that experience. Montana upland hunting varies too much: from summer like conditions to full winter; wide open prairie to your dogs rooting out wary roosters hiding in the cattails surrounding reservoirs and potholes.
However, I do think that whatever 28 gauge wand you have would be just about perfect for huns and quail in Montana or pretty anywhere else loaded with that #7 shot. There, I think, you could say it would be beneficial; you can end up walking a long, long distance on canyon and ravine and reservoir rims in northeastern Montana to get your chances at quail.
