Twist rate for 7WSM...

MikeW · #1 01-04-2002, 05:12 AM

I'm building a 7WSM and plan on shooting the
162 AMAX,162&168 grain Berger VLD's.
What twist rate would you recommend?

TIA

Boyd Heaton · #2 01-04-2002, 05:44 AM

I am having a 7mm Rum built.I too will shoot 162's.I told the people building it what bullet I wanted to shoot and they used an 8 twist.

Warren Jensen · #3 01-04-2002, 07:49 AM

Having a barrel cut with a specific twist for a specific bullet is a science. If you want a barrel that will shoot more than one bullet and bullet weight then you have to compromise.

My general recommendations for the two cartridges mentioned are: 1:12 is too slow, 1:8 is too fast. 1:9 or 1:9.5 is about right, unless you will use mainly lighter bullets, then 1:10. Remember, a bullet is at it's most accurate when it is "just stable" at the muzzle. This is usually considered to be a Stability Factor (SF) of 1.3-1.5.

A 1:8 would be appropriate for an extremely optimized and heavy VLD. A 1:12 won't stabilize some heavier 7mm bullets at moderate velocities.

Varmint Hunter · #4 01-04-2002, 01:53 PM

The Hornady 162gr A-Max is a very long bullet for its weight and diameter. As such, you will need a 9 twist or faster to stabilize it. According to Hornady, my 10 twist Hart barrel (7STW) will only keep this bullet stable for about 100yds before it becomes UNstable in flight.
I'd opt for the 9 twist which should be capable of handling most bullets up to 175gr. An 8 twist barrel may be good for a particularly long and heavy, special purpose bullet but I really don't see the practical use of it. [img]images/icons/cool.gif[/img]

MikeW · #5 01-04-2002, 04:56 PM

Thx. Guys.
This gun is for 1000 yrd IBS competetion
and long range Prairie dogs and coyotes.

I don't plan on doing any deer or big game hunting with it. That's the reason for just match bullets with a high BC.

I'm not really concerend with shooting any of
the lighter hunting bullets although it might
be fun to see just how fast I could push a
100 grian HP out of it.