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1-8 twist or 1-9 twist for 7mm Hornady 162Amax?

I was all decided on a 26" - 27" 1-9 twist Krieger barrel for a Rem 7mmMag project. I was surprised to buy Hornady 162 Amax bullets and find that a 1-8 twist is what's recommended on the box. I intend to fire these bullets about at max of around 3,000 fps (or whatever gives me the best accuracy.) Even Berger recommends a 1-10 twist for their own 168gr VLD bullets.

I hate to go against what Hornady says. What gives? I'm a little intimidated now about what twist to go with.
 
They will shoot fine in a 9 twist barrel, in fact I have no trouble stabilizing them in several 10 twist 7 Rem mags. My 7 SAUM Light Gun barrels are 9 twist and shoot the 162 Amax and Berger 180 VLDs well. Really don't understand the 8 twist recommendation.

James
 
Same goes for me. 162 Amax's and 180 JLK's out to 1000 yards, 30 inch Shilen Select Match, 1-9 twist, 7SAUM.
 
Most everybody in th UK shoot 162s/180 match bullets at 1000 yrds out of a 9 twist tube(30 to 32 inch ).
Border , Bartlin Krieger all are shooting well.
 
The new boxed ones still have 1 in 8 printed on them and my 32" Brux 9 twist still puts em in tiny groups just like always... I have a 32" 8.5 twist Brux I'll chamber the same way this fall and see if it's any better, but I really doubt it...
 
Admittedly I have little long range experience but when I use Brian Litz' twist calculator http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi it seems that the twist rate makes the most difference at lower velocities - like transonic.
As I played with calculations for a 1.315" 140gr Nosler CustComp in 6.5mm a 1:9" was considered 'marginal stability' at 1700fps while a 1:8" is considered 'stable' @ 1100fps so I took a few trips down Ballistic Lane to figure out what my bullet velocity at max ranges are to determine a suitable twist rate. I went with the 1:8" since I would cross 1700fps at ~675 yards if started @ 2750. Just my $0.02
 
louie, There is a slight bit of a difference in stability in a bullet fired out of rifle at low velocity and one that is fired at high velocity and then slows down. The rpm of the bullet (and hence stability) does not slow as much as the velocity. A bullet fired out at 3000fps out of 9 twist is spinning at 240,000rpm. Fired at 1700 it is 136,000rpm. I would guess by the time the first slows to 1700 fps at 675 yards it is still spinning at better than 200,000 rpm.

Gyroscopic force (from spinning) must be stronger than lift forces so as a bullet slow in velocity, lift forces are greatly reduced but gyroscopic force stays relatively high.
Cam
 
VaniB, I always go for the slowest twist that i think i can get away with .. To this end we have tested 9 twist then 9.5 / 9.35 to 9.85 GT / 10 twist / 10.25 and even 11 in twist .. 162 Amaxs of the right batch were successfull in all ,as a matter of fact the 162 redtip held the 1K group record at one time in an 11twist,go figure.. The 9 twist is plenty safe IMO..JR..Jeff Rogers
VaniB said:
I was all decided on a 26" - 27" 1-9 twist Krieger barrel for a Rem 7mmMag project. I was surprised to buy Hornady 162 Amax bullets and find that a 1-8 twist is what's recommended on the box. I intend to fire these bullets about at max of around 3,000 fps (or whatever gives me the best accuracy.) Even Berger recommends a 1-10 twist for their own 168gr VLD bullets.

I hate to go against what Hornady says. What gives? I'm a little intimidated now about what twist to go with.
 
very good advice said:
VaniB, I always go for the slowest twist that i think i can get away with .. To this end we have tested 9 twist then 9.5 / 9.35 to 9.85 GT / 10 twist / 10.25 and even 11 in twist .. 162 Amaxs of the right batch were successfull in all ,as a matter of fact the 162 redtip held the 1K group record at one time in an 11twist,go figure.. The 9 twist is plenty safe IMO..JR..Jeff Rogers

As far as i am concerned, the twist rate recommendations on bullet boxes should be ignored. A 300 whisper and a 300 RUM have comPLETEly different twist requirements for the same bullets.

In long-range shooting, over-twist adds more torque and more torque is just another in a list of variables that must be overcome in the pursuit of LR precision.

The 6mm 116 berger comes with a recommendation for a 7" twist, and yet they are shot from 6BR's using 8" twists quite regualrly. Furthermore, my testing of the 7" twist showed it was too much for that bullet in a 6-6.5X47 and a 6XC

RPM for given speeds seems to be a smarter reccommendation
 

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