Some older scopes were done in 7/8" tube dia that were quality pieces for their time- in the '30's and '40's-Lyman, Noske, Pecar, Norman-Ford and others had high quality scopes in this diameter. The only 7/8" tube I own is a Weaver V-22- a 3-6X from the late '60's-early '70's. The optics are clear and bright, and there is a plex reticle. It looks to be slightly better quality than the Bushnell zoom rimfire scopes from the '70's.
Weaver at one time made top detachable standard rings in 3/4" and 7/8"- they fit the standard Weaver top mount bases.
Regards,
Doc Sharptail