Sierra 6.5mm 130 grain TGK Twist Rate.

kiwikid

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Joined
Oct 21, 2012
Messages
542
Location
New Zealand
Hi Guys and Gals,
Sierra suggest that their new 130 gr TGK requires a 1:8" twist barrel but when I load the data into the JBM Calculator it gives me a stability reading of 1.690 as seen below.
I have two questions please,
1. Have I done something wrong with the info I have entered into the calculator?
2. Has anyone tried these in a 1:9" twist barrel?

Thank you for your time and help.
kiwikid.

Stability
Input Data
Caliber: 0.264 in Bullet Weight: 130.0 gr
Bullet Length: 1.380 in Plastic Tip Length: 0.210 in
Muzzle Velocity: 2800.0 ft/s Barrel Twist: 9.0 in
Temperature: 59.0 °F Pressure: 29.92 in Hg
Output Data
Stability: 1.690
29-Sep-19 22:26, JBM/jbmstab-5.1.cgi
 

kiwikid

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Joined
Oct 21, 2012
Messages
542
Location
New Zealand
Hi Lance, thank you for your reply. These bullets are for a older but modern factory rifle that unfortunately has a 1:9" twist. When I contacted Sierra they said they didn't think it would stabilize but the figures from the JBM look good to me.
 

kiwikid

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Joined
Oct 21, 2012
Messages
542
Location
New Zealand
I’m curious what kind of results you got with the 6.5 x 130 TGK.


My recent research indicates the JBM Miller/Courtney Sg calculator likely yields the “most accurate” results due to relevance of data input parameters.
The testing I did was shot through a Carl Gustaf 3000 (Colt Sauer 80/90) in 6.5x55mm with a 1:9" twist while working up a load using Rel 23 powder and my results were very positive.
My velocities ranged from 2560 fps to 2812 fps and all bullets displayed stability at the 100m target. At this stage I haven't shot them at any longer range.
The first attached photo is at 2783 fps and the second 2812 fps, both are 3 shot groups at 100m at an altitude of 500m (1640 ft ASL).

20200808_100049.jpg 20200808_100041.jpg
 

djfergus

Well-Known Member
Joined
Dec 25, 2015
Messages
1,878
Hi Guys and Gals,
Sierra suggest that their new 130 gr TGK requires a 1:8" twist barrel but when I load the data into the JBM Calculator it gives me a stability reading of 1.690 as seen below.
I have two questions please,
1. Have I done something wrong with the info I have entered into the calculator?
2. Has anyone tried these in a 1:9" twist barrel?

Thank you for your time and help.
kiwikid.

Stability
Input Data
Caliber: 0.264 in Bullet Weight: 130.0 gr
Bullet Length: 1.380 in Plastic Tip Length: 0.210 in
Muzzle Velocity: 2800.0 ft/s Barrel Twist: 9.0 in
Temperature: 59.0 °F Pressure: 29.92 in Hg
Output Data
Stability: 1.690
29-Sep-19 22:26, JBM/jbmstab-5.1.cgi
That 130 is pretty long. Its roughly the same length as the 135 atip and the atip is long for a 135gr. All you can do is give it a try.
 

Quintus

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Joined
Apr 15, 2013
Messages
542
Good bet they will work. I shoot the 130 Bergers from a 700 TI in 260 with a 9 twist and they are the most accurate bullets it shoots. They will stay inside 3" at 400 yards if I slow fire them and the holes stay nice and round. I'm at around 1100 feet and running them at a smidge over 2800FPS.
 

antelopedundee

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Joined
Oct 14, 2018
Messages
791
Location
Iowa
The first pic is of a target I shot recently using 58.5 grains of Reloder 22 in my 8 twist 6.5-06AI at 100 yards.

The second pic is with a load of 62 grains of H1000 from the same rifle on the same day.

The 3rd pic lower left group was shot about a year ago from my 9 twist 6.5-06.

If you can tell which one is more stable from looking at the bullet holes. well good luck. I expect that at reasonable ranges say out to 300 yards that one is about as good as the other. That particular 130 grainer could be on the cusp of being as well suited to one twist as to the other.





 

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