Twist rates...question

n/a

I just had a custom rifle built in .300 Win Mag A.I. with an 11" twist. Do you think this twist rate would be optimal for using 210's and 220 pills?

Last but not least, does anyone here know the twist rate for a Sendero in 7mm SAUM? Thanks!



Eric
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All American Arms Company

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nononsense

Eric,

The 1:11" twist for your cartridge is perfect when using the 210 or 220 gr. bullets including the VLD versions. I've been using the 210 VLD's for quite some time on several .308 cartridges from .308 Win. up through the .300 RUM and I've been getting superb performance out to (actually past) 1,000 yards. You will still need to run tests simply because each rifle and barrel are different and you might find that the 220 'such and such' doesn't want to perform in your system.

If long range is what you're "aiming at", then you should also consider the 190 class bullets as well.

If you're asking strictly about hunting weight bullets then there shouldn't be any problems at all with the twist rate.

Best.

JustC

The 190's up to 220's would be optimal in the 11 twist.

210gr berger
220smk
200smk
216gr clinch river


the sendero I beleive is a 1:9.25 twist. The 162gr a-max likes my 7mm rem mag barrel very much.

why chase the game when the bullet can get em from here?....
Got Balistics?

Ray B

I have no experience with this particular set of variables, but there is a formula for determining proper rate of spin; though I can't place the name of it just now. It involves the length and diameter of the projectile, and the velocity. The answer actually comes out in terms of calibers- that is, a multiplier of the diameter of the bullet.

sandwarrior

RayB,

The formula is called the Greenhill formula. T=150{D(squared)}/L
T=twist
L=length
D=Diameter of bullet.
use 150 for bullets under 2800 fps and 180 for bullets over 2800 fps.

ECC,

Using the Greenhill formula the bullets you describe work out methematically to about 10.9 something for rate of twist...so, like JustC and nononsense have said Those bullets are about as optimal as you are going to get.

I use a variation of the Greenhill called the velocity formula. where the 150 is substituted with the actual velocity.

It is T=.06 x V x D(squared)/L
the only change to the above is V=velocity.

I have taken and algebraicly refigured the formula to find the velocity I want to use as I already know the twist. That is
V=TL/.06/{D(sq.)}
So, you have an 11 twist x 1.4(L) / .06 / {.308(sq)}=V

I just plugged in 1.4 as an approximate,

V comes out to 2705 fps. That is the velocity you need for the optimal twist on the bullet in flight. You can go a couple hundred fps up from that and it will work just fine. -have fun

We have the second amendment so that all the rest are secure....UNK>

ContacFront

ECC,

I would say stay with the 190s and 200s, maybe 210 VLDs from Berger but I hear a lot of guys have problems getting the 220gn bullets to shoot well in 1:11 barrels.