Interesting point, the extreme cartridges may have different needs than the more moderate cartridges.
They certainly do !!!
The times that I have built "Extreme" rifle/cartridge combinations, groove design along with twist rate was a major consideration.
I have found that Bullets are the limiting factor if the wrong grove design is picked Irregardless of the twist rate and also the other way around for extreme cartridges.
I have had good results with the 3 grove design as long as I used strong or bonded jackets. Example: One such rifle with a 3 grove in 223 WSSM has exceeded 4600 ft/sec (Still not maxed out)with very good accuracy with good bullets. twist rate is 1 in 15 and at or around 4400 ft/sec It culled most jacketed bullets. I did not try Mono metal bullets because I wanted to see the effects of this combination.
I have found that in the middle of the diameter range and velocity cartridges that almost any grove design will work If the optimum twist rate is picked.
I also consider the truly big bores to have special needs like 8 grove barrels with slower twist rates because of the bullet mass and the starting inertia that causes the jacket to be separated from the core.
also as stated the land height is important. Most dangerous game bullets have heavy jackets and the multiple lands (8 or more) engrave well. This is what I would consider the perfect place for the gain twist
along with an 8 grove design.
Barrel manufactures will recommend grove designs and twist rates based on you needs but sometimes you have to think outside the box and choose what is best for your use.
Choose grove design and twist rate wisely and the outcome will be good. Choose poorly, and you will have a disaster in the making.
like most people that experiment have found including my self, mistakes are inevitable.
More to come
J E CUSTOM