more "proof"?
Digging to my in archives a bit more, I came up with an article I clipped from Guns & Ammo magazine written by Ross Seyfried. The piece is dated August 1987 and appeared in the "Proof House" portion on the magazine that reviewed new gear and guns. The article is simply titled "Ruger Mini-Thirty".
In the final paragraphs, Seyfried addresses the .310 diameter bullets of factory ammo, but states, "The Ruger rifle has a standard .308 inch barrel, but has a long throat to safely accommodate the standard military and commercial ammo with the .310 inch bullets."
I'd posted earlier that C.E Harris, worked at/with Ruger on the Mini30 and published a similar comment. Here is another printed statement indicating that, at one point in time, the Mini-30 had a .308 bore. Note this statement is made in 1987, 3 years BEFORE the 1990 Harris article. These are two separate, printed, published articles by established authors, not internet babble. Admittedly, Ross Seyfried was a gun scribe and not a Ruger associate, but he wrote well and was not prone to exaggeration or error. I alway liked Seyfried's articles, and this one on the Mini-30 convinced me I would have one some day. I hope they keep making it, but I am not so sure.
The Brownells commentary, and Rugers stance at this time, leads me to think that NOW the Mini-30 does indeed have a .310 bore , but there are very good indications that early on, some Mini's had a .308 bore...... whether Ruger will admit it, or there is anybody left that remembers.