I've asked this on another board so those folks bear with me

In selecting a barrel for a 300 Mag what would be your choice... 1-10" or 1-11"?

The specifics for my project would be a Pacnor #1, 23" in 300 WSM.

I haven't settled on 3 groove or 4 groove either. What are your thoughts there?

Bullets to be used would be 180's.

Looking at Dan Lilja's web site he states the twist really has more to do with bullet length than weight... a 180 Barnes X would obviously be as long as a conventional 200 grainer and therefore the 1-10" would probably be preferable. Ditto 180 Ballistic Tip's, etc.

Would a slower twist give higher velocity?

BA

Brad,

Given the choices you have, I would recommend the faster of the two. You may at some point wish to shoot bullets from the upper end of the weight scale and you may need every bit of spin that a 1:10 will give.

Will a slower twist produce higher velocities? No. The faster spinning bullet in open air is more efficient and less effected by the elements than it's identical slower moving counterpart, however, in a barrel where there is no place for the air that is trapped ahead of the bullet to go except ahead of the bullet, there is an increase in resistance and therefore the potential for increased pressure, VELOCITY, etc...

Regards,

Malm

Brad,

The standard twist for the .300 mag cartridges is 10" for a reason. Experience shows that you can shoot 200 or 220 grain spitzer bullets (i.e. long ones) if you want.

The shorter twists are usually selected for target applications where usually one bullet weight (and length) is chosen, and the rifle is fired at a given range. Some folks name this the "slowest twist" choice; you could say it is chosing the slowest twist that will do the stabilizing in air for the velocity range employed.

Winchester's testing of the number of grooves versus accuracy in the .300 WSM showed the 4-groove barrel to be more accurate. I know reports say they tested more groves than four, but I don't know if they tested a three-groove barrel.

I would go with the 10" twist barrel with four grooves and lands. But heck, if you want something different, a three-groove, 11" twist barrel would be that.

jim dodd

Malm... good explanation. Thanks.

Jim... you're right of course. Olin did settle on the 4 groove 1-10" for solid reasons. In fact this year Douglas released its first four groove barrel... in 308" only. I doubt that's a coincidence! I'm not much on reinventing the wheel (and beleive I may have "over thought"this whole thing). You're right, a 1-10" 4 groove is the way to go, particularly as I see little need for bullets under 180 in this rifle. Thanks.

Brad

There is a formula in Hatcher's Notebook for calculating the correct twist for a given bullet. As I recall, it has more to do with the length of the bullet for a given caliber than anything else.
What I do remember is the answer for the sample given which was for the 220 rn military bullet which was 1.35" long and requires a 1 in 10 twist.

I know that doesn't help a whole lot, but if you have access to a copy of Hatchers you can look up the formula

Unless the customer has a specific rate of twist in mind for a particular weight bullet or a specific purpose for the weapon, and the weapon will be used for hunting a variety of game, I will generally recommend the fastest twist available for that caliber because people change their minds and I think it is better to have the additional spin and not need it, than to need it and not have it.

Malm