MINI THIRTY 7.62X39MM GROOVE DIAMETER

BULLETS & BRASS

- Brian Pearce

Q: I enjoyed very much your article about the Ruger Mini14 and Mini Thirty rifles in Rifle No. 308 (January/February 2020). I have a Mini Thirty that I received as a Christmas gift in 1986 or 1987. I believe it to be one of the first to leave the factory. I have read previously about the .308 inch groove diameter that you mentioned in your article. In slugging the bore it indicates that my rifle does indeed have a .308 inch groove diameter. I am very curious to know where you received your information. Best Regards.

S.R., Licking MO

A: This dates back many years ago when I was trying to develop handloads for a Ruger M77 Mark II chambered in 7.62x39mm. I contacted Ruger for some technical details and was told the company was in the process of changing the groove diameter for all rifles in that caliber to .308 inch, including the Mini Thirty and M77 rifles. That change would begin in 1990. Previously, Ruger used a .310- to .311-inch groove diameter.

As an interesting note, in the book Ruger & His Guns by R.L. Wilson, he indicates that the Mini Thirty was introduced in 1991, but most sources list 1987 as the year of introduction, which corresponds with your memory of the year you received your Christmas gift. Incidentally, you can contact Ruger Customer Service (603863-3300) with the serial number of your rifle and they can give you the date it shipped from the factory.