Have been shooting the 7mm STW in a Sako 75 stainless for years with excellent results.
Recently I have started using the Barnes 175 gr. TSX and it seems some bullets enter slightly off balance. The groups are good if I do my part and game I shoot is as dead as any but I´m wondering... I believe the twist rate is 1 in 9,5. Anyone have an experience with this ?

Never had a factory STW keyhole but never used 175 Barnes.

If you have room you might try a higher velocity.

If you hit what you shoot at live with it. Or drop back to a 160gr if you are concerned.

Those 175 grain TSX are really long and you are probably not stabilizing them perfectly.

Shoot some groups at 200 - 300 yards and see how well they do.

Not the Barnes bullet but Sierra warns 8.5 or faster twist for 175 grain bullets. Barnes all copper are longer than the SMK so I would say 9.5 twist is to slow.

Someone put link to a Miller's Twist Rate calculator in Excel in a different thread. At 3100 fps, this is a marginal bullet for stability. I don't think you can drive the bullet fast enough to stabilize it in a 9.5 twist barrel.

www.accurateshooter.net/Blog/millerformula.xls

Hate to say it but I agree.

What distance are you shooting?

100-200m

Google JBM Ballistics. They have a stability calculator. It is not the old Greenhill. I think it is the Miller formula. You will need twist rate, ballistic coefficient and bullet length. Note that standard temperature and pressure is entered automatically. Standard temperature is 59.xxF,so insert the temp at which you hunt. I like to see a stability factor of at least 1.2, but there is no set standard.

quote:

Google JBM Ballistics.

Thanks. I use JBM all the time but have never went to the bottom of the page. Seems like it calls the 175 in a 9.5 marginal assuming 3000fps. Would get worse if velocity is less

Shoot the 160s and problem solved unless you have a bad barrel...

The 160 shoots flatter and I can't think of an animal specific to the 7mm STW that it won't shoot through lengthwise including the big bears of Alaska.