I am in the process of ordering a Pac-Nor .375 bbl. I was wondering what twist rate 1-12 5 groove or 1-14 6 groove?, and whether a guy needs a 5 or 6 groove. Whats the advantages & disadvantages between the two?

I will be shooting 270 or 300 gr. bullets

Thanx.

1:12 is better for heavier bullets.

Agree with the 1:12" twist being better. It will handle 300-grain monometal copper bullets and 350-grain lead-cored bullets.

1:14" twist may cause stability problems with the above bullets but work well with 300-grain lead-cores.

5-groove versus 6-groove is no big deal.
6-groove and 1:12" twist would seem to be the most common, i.e., the "universal" .375 barrel.

How well does the 12" twist do with the rino 380's? what is best for those?

I will stay with the 1x12, as it has worked perfectly for me with 250 to 350 gr. bullets.

This twist thing has been around for many years and its been tested and re tested, its nothing new, I used to argue this with my old buddy George Hoffman, I told him the big boys had already done all his work for him, then he went off into this tirade of explanation that left me in a state of wonderment! Damn I wish I could listen to one of those sermans just one more time..

There is a formula which I don't recall but you can find on the internet that when worked out says a 1 in 14 twist SHOULD be better for 300 gr LEAD CORE bullets. My M70 barrel is the "standard" 1 in 12 and has worked fine with anything put thru it 235- 350 gr lead cores or Barnes TS 300gr. The longer bullets like the 350 Wodleighs shoot great in my rifle and the even longer Barnes TS do also. If anything would give you a problem, according to the theory it should be the shorter bullets but the 235 gr Speers shoot fine in my gun so it seems to be much ado about nothing.