I recently purchased a used but not abused older Ruger 77 with the tang safety -7 Mag. After briefly range testing it (3 groups of 3 ea), I was pleased to see it will shoot 3/4 to 1 1/4" groups.

Later at home while cleaning it up, I noticed the barrel rifling is much different than my other newer Rugers, and different than my old Model 77 243 which is also from the tang safety days.

The rifling in this 7 Mag somewhat resembles Marlin Micro-groove - it has about twice as many lands-grooves as my other Ruger rifles, and it appears to be less deeply cut than the others. It's a genuine stamped "Sturm Ruger and Co, Southport, Conn." barrel, so it's not an aftermarket.

Can any of you Ruger experts give me any information on this type of rifling, what it's called, why it was used, why they stopped using it, etc.?

I'm certainly not a Ruger expert but I have heard from the guys in the know that Ruger farmed out their barrels for a while in the early days of the rifle building, so it could have been made by any number of barrel makers.

Ruger regularly used "Micro-groove" barrels on their .375 and .458 rifles. Didn't know they ever used them on other calibers.

News to me too. I have a couple of Marlin lever actions but both have Ballard type rifling so I have no experience with "Micro-groove".

Seems to work just fine in this 7 Mag. The three groups I shot were with a load I had specifically worked up for my other 7 Mag, so it was more of a function test...best group was about 3/4". Looks like it won't be too difficult to fine tune this one.

Thanks for your responses.

Ruger is not the only big company other than Marlin to experiment with "micro-groove-type" rifling.

For part of one year (1979) Remngton Model 700-V rifles in .308 came with Remington factory-made 12 groove barrels. The one I owned is now the property of a fella in Sutherlin, Oregon.

It was/is a very accurate rifle also. It won the first 7 consecutive "hunter-benchrest" matches in which it was shot.