I am about to build a .300 H&H however, sometime down the road, I may rechamber it to .300 RUM.

In either case I never shoot bullets in excess of 180 grains and really like to shoot 150's and 165's.

My question is what rate of twist should I use. My .300 RUM has a twist of 1 in 12. My .300 H&H has a twist of 1 in 10.

Which should I use? I would appreciate the forum's thoughts.

Thanks in advance.

Always error on the fast side. The standard is 1-10 and that seems fine to me. What with some bullets made from metals lighter than jacketed lead today I would not go too slow.

If it were a target rifle made for a particular bullet then I might get more specific. Also when a barrel wears the faster twist will shoot well longer.

Re Savage99's comments, sound wisdom there. Also
bear in mind, that rate of twist is primarily a
function of bullet length, not weight. 20 yrs ago
wasn't that big of deal. In order to have a certain weight, most bullets were fairly close to the same length when compared according to style:
spitzers compared to spitzers; round nose to round
nose.
With the Barnes X-Bullet and Swift's Sirocco, these bullets, say in .284 dia, the 150 grainers
are the same length as Hornady's 175 grain. So faster (rate of twist) is definitely better than slower.
What I think (probably wrong) that Remington
is doing with their 300 RUM is taking into consideration the velocity of their cartridge and
calculating that they can get away with the slower
rate of twist. Also, slower rates of twist often
produce a bit higher velocities. Personally, I hate when a rifle mfr limits the versatility of a cartridge because someone back at the factory
"figured" that most shooters would use a lighter bullet (less felt recoil).
Note that the 300 Weatherby, no slouch in the velocity department, also uses a standard 1:10 rate of twist, and does very well with the full range of 30-cal bullets.
You also have the added advantage of not having to
rebarrel, you can merely re-chamber the 300 H&H to
the 300 RUM.

Savage99 and ancien-

Thank you for your comments.

ancien,

I am not an engineer or a balistician. I was curious regarding your comments regarding the Weatherby cartridges. I was always told or understood that the way Weatherby rounds acheived their velocities, given their rates of twist, without over-pressure, was due to the amount of free-bore in their chambers. Thus the implication was/is that to achieve those velocities absent free-bore, you had to use a slower rate of twist. What are your thoughts?

Thanks,