To add to what Delmonico wrote and about 40 Rod's comment:
The reason (I've heard) that most brass shells weren't common here until WWI is because the US Army was using 12 ga. paper shells in their 'trench guns' until during the War. Then, thanks to trench warfare and related weather problems, they found that the moisture swelled the paper shells and caused feeding/extraction problems on a major scale. 'Thru VietNam and into the 1980s, these all-brass rounds could still be found in the Military for Ammo guard, etc. Now, most are plastic but it wouldn't surprise me if I found out that there are
still some being made for SEALs, Rangers, Delta Force, Special Forces, etc. and other "special" uses or specialty ammo.
To add to Silver Creek Slim's post: Midway USA (and others) sell those Magtech shells in most gauges, not j
ust 12 ga. There are also American companies who sell machined brass shells, but they are double to quadruple the cost of the Magtesh shells. As a point of intrest, the Magtechs are 'Balloon-Head' cases, essentially the same as the "Olde Tyme" ( sp.
) cases were during the late 1800s. This also means that they are thinner and
technically not as strong as the machined types, but that doesn't seem to be a problem, as some folks load them up with smokeyless powder - not just Black Powder; which, I'm sure, is used in MOST of the brass cases sold. Like mine.