Help with Barrel Twist Rates……

[RugSnacker]

First off, I want to profess my ignorance on building a rifle………….but, I figured I would give it a try, rather than buy another production rifle. I intend to use this new rifle primarily for hunting, but will surely shoot far more rounds at the rifle ranges. I have decided to build either a 300 Win Mag or a 300WSM (depending on what action I buy). My intentions are to purchase all the required components as I get the “disposable” funds available.

I have purchased an unfinished 28” SS .30 caliber barrel from the Montana Rifle Company.
The barrel is a 1-12 twist.
Since buying it, I have chatted with a couple people who have told me that 1-12 twist may be too slow………

It was my understanding that the primary concern with twist rate was to achieve gyroscopic stability (SG)…….where you want an SG greater than 1.40 and less than 2.0.
When I plugged a 168gr VLD Hunting Bullet into Don Miller’s Twist Rule changing only the twist rate, I get the following:
• 1-10” twist, 168gr VLD, 0.308 caliber, OAL 1.265, 3000 fps, 59F, 29.92 in merc. = SG of 2.28
• 1-12” twist, 168gr VLD, 0.308 caliber, OAL 1.265, 3000 fps, 59F, 29.92 in merc. = SG of 1.58
From this, I figured a 1-12” twist would be better than a 1-10”………

Have a screwed up buying a 1-12 twist??

Thanks in advance for any input……….

 

[mouse07410]

Re: Help with Barrel Twist Rates……

I wouldn't say SG <span style="text-decoration: underline">must</span> be below 2.0 - but it's nice to keep it there. When SG falls below 1.0 - the bullet becomes unstable.

If your calculations are correct (I didn't bother checking them), 1:12 twist is just fine for the bullet you're considering.

If you don't have Bryan Litz's book yet - do yourself a favor and get it. You won't regret it.

 

[ROTTEN TREATS]

Re: Help with Barrel Twist Rates……

ive got 308 win rifles with 1-12 twist rates and they work at thair peak with 168 gr bullets so the higher Velocity of a win mag might need a slower twist if anything. i think you will be just fine with 168s and up

 

[RugSnacker]

Re: Help with Barrel Twist Rates……

Thanks for the input..........
I didn't know if there was more things to consider than I missed.
I think most 30 caliber "factory rifles" come out with a 1-10 to stabilize all possible bullets (including the largest).

I knew the 1-12 was not standard, but thought it would be fine........and actually better for the smaller bullets..........say 175 and under.

 

[RADcustom]

Re: Help with Barrel Twist Rates……

It should be fine. You may be limited on how heavy of a bullet you can shoot, but if you plan to stay with the lighter bullets it shouldn't be a problem.

300 WM and WSM are typically 1-10 for shooting the heavier 190gr and up bullets.

 

[RugSnacker]

Re: Help with Barrel Twist Rates……


Thanks..........I guess I will continue on the path I am on.
Now I just need to find the Action, Stock, etc. at a reasonable price.

 

[wildbill9ball]

Re: Help with Barrel Twist Rates……

look in to 155gr I use 168 in my 308 and a 1-10 Krieger but at 2700fps anything beyond 900yds is key holed from what i have read 155 would be great for 1-12