MSUMarksman,
JDJones is right on with his comments as far as I am concerned.
Only time I do not use a 3 groove rifling design(Lilja) is when I will be driving a very heavy(long) J-4 jacketed bullet fast in a fast twist barrel.
The upper end range for a 3 groove barrel with a J-4 jacketed bullet seems to be 1-8 twist and around 3200 to 3250 fps. The SMKs allow significantly more velocity before being effected by the 3 groove as far as bullet failure.
In your case of the 280 AI. If your going with a fast twist barrel I assume you will be using heavy for caliber bullets as in the case of that chambering you will not have the velocity potential to do any damage to any bullet out there in the VLD or ULD design on any jacket that is currently being used.
The 280 AI is very bullet friendly, even with the heavy thin jacketed bullets so your selection of rifling design is not all that critical.
I have heard reports that the 5C and 5R barrels will get to significantly more velocity and less pressure then a conventional 3 groove barrel such as that from Lilja, I have not seen this with actual tests.
I actually tested a Broughton 5C barrel in 6.5mm and a Lilja 3 groove barrel of the same caliber, both chambered in 6.5mm WSM. The Broughton was advertised to make it impossible to loosen a primer pocket using appropriate powders for the selected round being used.
Well, I loaded up the Lilja barrel to top end loads and then did the same with the Broughton and in once fired cases, the Broughton barrel was loosening primer pockets with one grain less powder then the Lilja was.
This was not just a one shot test, this was an average of five cases at each load level. Same brass, same powder, same bullets, same exact chamber and throat.
Simply put, they were so **** close to identical it was not even worth comparing but the claims you can not loosen a primer pocket with the 5C barrel was not legit which I never beleived for a minute.
As far as accuracy was concerned, both barrels were 15" barrels on XP-100 handguns. They both were averaging in the 1 to 1 1/4" range at 300 yards so there was no sign that one was more accurate then the other, both shot amazingly well.
Simply put, with the chambering you are going to use, take your pick, it will not be critical in the 280 AI. Get a Lilja, Broughton, Rock, Krieger or Hall and you will be happy with the results if it is machined correctly on a square receiver.
Good Shooting!!
Kirby Allen(50)