What the above guys said.
H&R built single shots in 22 and 17 rimfires, various centerfire rifle cartridges from 22 Hornet to 45/70, and shotguns from 9mm shot to 410, 32, 28, 20, 16,12, and 10ga. All on the same size frame. Steven/Savage did the same with fewer rifle cartridges offered.
One size OD with many different sizes of ID all fit on the same size receiver meant one set of internal parts, one size stocks and maybe two or three various forend contours to accommodate the larger or smaller barrel channels.
Generally they were made to be cheap and profitable, not necessarily well balanced or svelte.
