On the Brass shells, I have only a very meager collection of them but all the old ones I have (also newer ones) in 12ga measure just under 2½" thus should be suitable in virtually any 12ga except a 2" chambered one. I have no idea why Parker added the caveat about their use with smokeless powder. One of my "Thin Brass" shells is plainly marked on the head UMC Co/No 12/Smokless. My very first experience in reloading was done using all brass shells with DuPont Bulk Shotgun Smokeless. Info for so doing was taken from a Lyman loading manual from the late '50's.
In 10ga I have all brass shells measuring "Just Shy" of 2½", 2 5/8" & 2 7/8". I assume that 12ga brass shells were made in longer lengths than the 2½", I just don't happen to have any.
Due to the extra internal capacity a heavy 1¼ oz or even a magnum load can be put up in these 2½" brass case, but that doesn't mean of course they should be fired from a light 2½" chamber gun proofed for the standard load for its length.
All of the brass shells I have are for standard chambers, I don't have any of the ones for the smaller chambers.
