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Posted: 8/4/2016 9:52:45 PM EDT
Hy friends.
I am starting to compete in bench rest with my steyr ssg 69 on 308 so my concern is to get the most small groups as possible.
At the moment I make 5 shoot groups in 2 inches at 300 meters(1/2 MOA) in this conditions: about 11.000 ft high. (Andean mountains) 670 mbar 15 to 18 deg celcius.
Sierra match king BTHP 175 gn 2350 fps.
At this distance, shoots are in the winning zone, but a very small variation can place one hole otside of the center, orvthe group will not be so nice at 400 meter and londer distances.
So I was reading a lot of stuff, and twist /stability is one of my concerns. I found the Bergers calculator which tells me the stability of my bullet is very very good, but other articles recommend a twust of 1:10.
I know twist rate vs bullet weight is an allready discussed theme, so my question is about your experiences with the reliability of this calculator, but I also hope you can share your twist rate/bullet weight experiences at medium and long range shooting with 308 if you also have a 1:12 barrel
Thanks a lot
Link Posted: 8/7/2016 12:36:20 AM EDT
[#1]
If your inputs are correct, you could use a 1:15 to properly stabilize the 175gr SMK and get the maximum B.C. without any extra yaw/wobble nonsense.



Berger and JBM are showing about the same results.
Link Posted: 8/7/2016 8:33:19 PM EDT
[#2]
Yes. Inputs are correct.
I think we shoot at the highest range of the world here in La Paz.
Link Posted: 8/9/2016 9:25:09 AM EDT
[#3]
would love to see some pictures posted of your range!


berger's twist rate calculator has always worked for me.  if it says it will stabilize it, it should.  I think they recently started recommending more twist than they used to and litz did some study on the effects of over stabilization which were very minor iirc
Link Posted: 8/9/2016 4:53:01 PM EDT
[#4]
Its somwhow difficult for me to place puctures. But take a look on google maps club hipico los sargentos la paz bolivia. We use the shooting range they have.
Link Posted: 8/10/2016 10:14:05 AM EDT
[Last Edit: popnfresh] [#5]
I ran 185 juggernauts and  berger 210 gr lrbt in my 20" 12 twist 700 at sea level. Now with a 10 twist I shoot 230otms.

The 210s were not 1.5sg but grouped well. The 185 s I used for 1k.




I shoot the 230s to 1100 and the predicted drop is correct so I suppose I am getting the full BC so it should be 100% stable as predicted by the stability calc.
Link Posted: 8/11/2016 7:46:51 PM EDT
[#6]
Thanks for the posts.
I am happy to know Ibwill be able to use my 1:12 and will not need ro search for a 1:0
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