For what it's worth, I have had 3's, 4's, 5's, 6's, and 8's. I have looked at all of them with a borescope throughout the duration of their lives and can honestly say that have not seen any one last longer than another. Some very highly regarded people stand by the 3 groove for improved life but I personally have not seen it happen.
I will say that the lands in the leade of a 3 groove barrel do stay in place longer thus making it so you don't have to chase them with the bullet. However, they still get heat cracking just the same as all the others and once that happens, they actually become <font color="blue"> harder </font> on the bullet than the others.
You could have a rifling as wide as an I-beam and if it is exposed to super heated gases long enough it is still going to ruin the steel. The melting point of steel is less than the temperature of the expanding gases and it won't make any difference if the land is 1' wide or .010" wide. It will still melt.
I have personally witnessed one barrel of my own and two barrels of my uncle's that were 3 grooves and wow did they like to blow up match bullets. Hornady Amax barely made it through the chronograph. Bergers made it to about 50 yards. And Sierras MK's actually shot fine for a few hundred more rounds before they disintegrated before the 100 yard paper.
4 groove were better, but 5 grooves seem to be the best middle ground. My 8 groove was gentlest on the Amax, but it did have to be seated farther and farther out. No big deal, I think it is easier to adjust the seating stem on the die than to deal with bullet blowups. /ubbthreads/images/graemlins/wink.gif
Now, the Mike Rock and Broughton barrels can be ordered any way you want, but they do advocate the 5 groove for reasons mentioned earlier. It seems to give higher velos because of the canted design and reduces wear on the bullet because of the opposite side riflings inherent to the odd numbered grooves. These observations have been justified by many shooters. I have had a 5 groove barrel, but it was not a 5r or 5c. It shot fine and seemed to be gentle on the bullet but it was not faster than any other grooved barrel.
I do have a 5r Mike Rock now and I will be experimenting with it shortly in all these areas to see if what they say is true. I will post my findings in "bullets, barrels, and ballistics" under "338 thunder project" as soon as Kirby gets it chambered and threaded. /ubbthreads/images/graemlins/wink.gif It should prove interesting at least.
On a side note, some people may be interested to know that Broughton used to work for Mike Rock and split after unresolved disagreements. According to Mike, his barrels are made better as they are the originals, not the immitators. That was his words. Many satisfied customers have Broughton though.
Mike's barrels are made on a modified Pratt & Whitney single point cutting machine identical to the one Kreiger uses. Only diff according to Mike is he makes more cuts with less material removed in each cut for a less stressed and smoother barrel. We shall see soon. /ubbthreads/images/graemlins/wink.gif
