Redhead, It's 5 lands and grooves with a slanted side on the land walls. The R is for Russian, the originators of the design. ( I read that somewhere ) There are lots of bbl makers doing their own version of this style.
Rock Creek-- 5R = Russian
Satern ------- 5S = slanted
Broughton -- 5C = canted
Shilen -------- Ratchet , and many others. I was told a few days ago that Kreiger was doing one now also but I don't know that to be true.
They work well and claim to give higher velocity with less jacket deformation because of the slanted lands and the fact that there are no lands directly opposing each other in the bore.
Lots of guys here on LRH are using these bbls with good results, I'm sure they will tell you why!!
+1 with 7mmRHB. That's pretty much the way I heard it to. I only have one 5R barrel and it's in a 308 Win, but I have been so impressed with the way that gun shoots, I ordered a Brougthon 5C for my 300 WM. The barrel is being installed as we speak.
As mentioned, the lands are not opposing each other with the odd number. I've always had an idea that was one of the main reasons why they are so accurate.
I've also heard very reputable shooters on this and other sites say that the number of lands doesn't matter all that much. They all shoot good as long as you get a quality barrel. In either case, I have been very happy with mine.
I have a 5R Bartlein ordered for my 300 Sherman and can't wait to get it installed. Lonnie Hummel at Hornady shoots one in 1000 yd. competition and loves it. He says they are a breeze to clean because the copper doesn't stick as easily (less angle between the lands and grooves). I too have heard of greater velocity and less bullet deformation.. Makes sense!........Rich
I think Barret (Boots) Obermeyer first used this in his cut rifled barrels for the 7mm Rem. Magnum barrels. Sierra's jackets on their 168 gr. 7mm match bullets were thin enough to be weakened too much by conventional rifling; they came apart spinning so darned fast. Obermeyer dubbed it "5R" and the rest is history.
I've used some 30 caliber 5R barrels from him in competition; great accuracy and decent barrel life.