Straight from Boots' website:
What does it mean when a barrel is said to be a "5R"?
5R is the form of rifling I developed for use in most target barrels and in many sporting barrels.
These barrels have 5 grooves, and the lands have angular sides. I have observed that bullet jackets
will deform such that they remain closer to the R-form lands than they will to the sharp-edged
lands present in conventional-style rifling. This reduces powder fouling at the corner of the
grooves. The angled form of the lands also helps to reduce jacket failures in quick-twist barrels.
I don't see anything in Boots' answer about the rifling having to be cut.
