The Accurate Reloading Forums
7mm STW keyholing
11 October 2015, 23:24
Adventura7mm STW keyholing
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 ?
11 October 2015, 23:49
ramrod340Never 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.
As usual just my $.02
Paul K
12 October 2015, 01:15
FjoldThose 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.
Frank
"I don't know what there is about buffalo that frightens me so.....He looks like he hates you personally. He looks like you owe him money."
- Robert Ruark, Horn of the Hunter, 1953
NRA Life, SAF Life, CRPA Life, DRSS lite
12 October 2015, 02:41
SamNot 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.
A bad day at the range is better than a good day at work.
12 October 2015, 02:50
SamSomeone 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
A bad day at the range is better than a good day at work.
12 October 2015, 03:18
LeopardtrackHate to say it but I agree.
13 October 2015, 08:50
RapidrobWhat distance are you shooting?
Gulf of Tonkin Yacht Club
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President NM MILSURPS
13 October 2015, 13:15
Adventura100-200m
14 October 2015, 17:06
BriceGoogle 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.
14 October 2015, 19:25
ramrod340quote:
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
As usual just my $.02
Paul K
21 October 2015, 01:06
AtkinsonShoot 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.
Ray Atkinson
Atkinson Hunting Adventures
10 Ward Lane,
Filer, Idaho, 83328
208-731-4120
rayatkinsonhunting@gmail.com