What is everyone's opinion on 5R rifling versus rifling with
six grooves, or other even number of grooves? Thank you.
(Caliber will be .375 H&H)

This said,

http://faxonfirearms.com/blog/...-and-why-5r-rifling/

... there are advantages to 5R.
Only disadvantage I see is that the odd number of grooves makes it harder to slug the bore to check groove diameter. You will need advanced mathematics or special slug-measuring jig to check the groove diameter.

I ordered 5R from Krieger for my .264 Ripmoor wildcat.
I noticed nothing special about lack of fouling,
only that it has no remarkable fouling issues.
But it is the only Krieger I own.

My Ruger RPR in 6.5 Creedmoor has 5R and my Ruger American Predator in 6.5 Creedmoor has 6-groove/standard rifling of same twist, and I assume same bore and groove diameters.
Both those Ruger barrels have the same muzzle diameter too.
They both shoot the same size groups with Hornady factory, match-bulleted ammo, point-threes for three shots at 100 yards.
I have not shot them enough to notice any difference in the fouling.

Whatever turns your crank, but in a .375 H&H I think you would never see any detectable difference between 5R and standard 6-groove.

A 6-groove, 1:12" twist, stainless, .375 barrel from Winchester is the most accurate .375 barrel I have ever shot,
a point-one with a .375 Weatherby re-chambered .375 H&H.
But the bullet used is more important for accuracy than the barrel.
Shooter, ammo, barrel.

A 5R of same twist and contour might be just as accurate, might even foul less.
But how much does that matter?
Give it a try and let us know.
I wouldn't turn one down if someone wanted to give me one.

Rip ...

I've got them in .308 and .300WM. Easiest barrels I own to clean and very accurate.

I Thank Both Of You For Your Posts!

Rip ...