Finally got to feeling better enough to get out to the shop and do some investigating on the RIO shot sizes, as loaded in their 1 oz. and 1 1/8 oz. target loads, blue box and brown box respectively.
Here's what I found by dumping shot, counting out twenty (20) shot pellets, and weighing the lot to get an average weight for each pellet, then weighing the entire shot charge.
RIO (blue box) 1 oz. / #7 1/2
20 pellets / 23.0 grs. = 1.15 grs. each
weight of payload - 425.5 grs. (12 grs. light of 1 oz.)
RIO (brown box) 1 1/8 oz. / #8
20 pellets / 19.1 grs. = .955 gr. each
weight of payload - 473.1 grs. (19.1 grs. light of 1 1/8 oz.)
What we can see from this is that the # 7 1/2 shot, as loaded in this RIO load, is very close to the Eley chart size for #7 1/2, which should weigh 1.12 grs.
Also, the #8 shot, as loaded in this RIO load, is very close to the Eley chart size for #8, which should weigh .97 gr.
Looks to me like they are loading pretty nearly true European sizes in what they sell from here to Texas.
SRH
That's all well and good as long as the shot is the same alloy. The differences in specific gravity between low antimony shot and high antimony shot can cause differences in weight of more than a few percent.
