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Discussion Starter · #1 ·
I'd always thought my 189 series, made in 1991, stainless Mini-30 has a .308 bore, so I e-mailed Ruger requesting the bore size and got this response:

"Pre-1990 Mini-30s were .308"-.309". After 1990 they were .3000"- 3015."

I suspect the post-1990 bore size stated to be .".3000" actually was meant to be ..3010". When I run out of .308 bullets, I'll switch to .311, unless there are comments suggesting otherwise.

Comments?

Thanks, Ralph
 

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Major General Chit Chat
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That is correct... sort of, but I'm reading through your typo.

CE Harris, who worked for Ruger when the Mini-30 was being developed has said a couple times in old magazine articles that there was no hard cutoff date from one bore size to the other. The first Mini-30s had a land diameter of .300 and a groove diameter of .3085, with a tolerance of .308 to .309.

The M77 in 7.62x39 had a land diameter of .3015 and a groove diameter of .3095. In the early days Ruger would use barrels made for the M77 interchangeably and concurrently for the Mini-30. Some with 189 series barrels with grooves that measure .310 with inexpensive calipers my actually have .3095 grooves.

Currently the SAAMI standard for 7.62x39 is .300 lands and .310 grooves, but there is some wiggle room and still variance in barrels made today.
 

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Bullet diameter is another can of worms. Harris and others also performed tests as early as 1987 that showed bullet design was more important than diameter. In one of his tests the 308 Sierra 150 gr Matchking handloads were more accurate in his .312 grove test barrel than the .311 Lapua control cartridge. Mini-30 owners have discovered that for themselves over the last 30 years.
 

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Discussion Starter · #5 ·
That is correct... sort of, but I'm reading through your typo.

CE Harris, who worked for Ruger when the Mini-30 was being developed has said a couple times in old magazine articles that there was no hard cutoff date from one bore size to the other. The first Mini-30s had a land diameter of .300 and a groove diameter of .3085, with a tolerance of .308 to .309.

The M77 in 7.62x39 had a land diameter of .3015 and a groove diameter of .3095. In the early days Ruger would use barrels made for the M77 interchangeably and concurrently for the Mini-30. Some with 189 series barrels with grooves that measure .310 with inexpensive calipers my actually have .3095 grooves.

Currently the SAAMI standard for 7.62x39 is .300 lands and .310 grooves, but there is some wiggle room and still variance in barrels made today.
Thank you, Beck. Good response.
 

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Major General Chit Chat
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The 189 Series was made from 1987 through the year 2000. My 189 series just happened to be made in July of 1989 and has a groove diameter of .3089. Others that have early 189 series have different land and groove diameters. There was lots of variation.
 

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Hmm. Mine is a 1990. Late year going by the numbers.
Yep the 1990 189s started with serial number 189-25005 and ended at about 189-38804. But Ruger does caution that their serial number system hasn't always been consistant over the years. Those numbers are usually close enough, but may not be exact. The earlier ones were better tracked, so you can be pretty sure yours is from 1990 and from the month Ruger has record of.
 

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"OTM's ?" Isn't that what the Border Patrol calls "Other Than Mexicans ?"

The 189 series Mini-30 had a long run, and four that have passed through my hands (two I still have and will always have, the third is with my daughter and son-in-law).
They ranged from 1989 to 1995 for production.
The earliest from '89 has a .309.5" barrel as do the others.

Ruger Mini Thirty Serial Number History
 

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if memory serves the early 30s had a longer chamber throat to 'squeeze' the bullets from the .3105 rounds available into the .308 groove bore.
don't fathom why but Nosler 308 bullets 125 gr (expensive) dropped on target compared to other .308 bullets, the 2 others are the 147 gr FMJBT meant for '06 loads (grouped well BTW) and Speer 150 gr FB SP I loaded for game, mainly white tail and feral boar- they grouped well enough for hunting, I shot just on paper so far.
mine is the later .310 groove dia.

Dog I like the wood stock 30 pictured, the plastic do not show the screw for the inner liner? what gives?
 

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During a long call to Ruger 2nd tier support last year, I was able to glean that the design of the chamber and long throat is still the same regardless of barrel land and grove diameters. It's still used today.
 

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Umm, may be a reason the 147 gr I had to seat out to just barely fit in the mag shot as well as did. I used the Lee factory crimp die just light crimp.
 
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