Cooey 71 .308 Rate of Twist

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lineofsight

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Just curious as to the rate of twist on my Cooey 71 in .308.

Am confident that a CGNr can provide a more accurate answer than the one I would come up with by trying to push a patch through the bore and counting rotations.
 
Actually you only count one revolution and measure how far the rod travelled... but you do need a good quality rod that rotates freely.

It is an accurate measurement.
 
I was thinking count revolutions and divide by barrel length but only counting one likely increases accuracy of the measurement. During cleaning not notice even rotations hence apprehensive about he approach - cleaning pistols notice rod rotation much more.
 
Most probably a 1:12. Good for up to 200 gr, so long as you avoid the VLD match bullets. I have shot some 220gr round nose in mine, just to see if it would work. no problem with accuracy, but probably too slow for bullet performance.
 
lineofsight said:
Just curious as to the rate of twist on my Cooey 71 in .308.

Am confident that a CGNr can provide a more accurate answer than the one I would come up with by trying to push a patch through the bore and counting rotations.
Click to expand...

No-one here can provide a more accurate number than you can by doing what you have suggested. If you come up with 1:11.8 and it's actually 1:12 so what? There could have been barrel twist options or a changed out barrel, or the info someone passes on could just be incorrect. If someone says 1:10 and it's actually 1:14 then that's a big deal.

Seriously, spend the 5 minutes and find out for sure.
 
A bullet gains gyroscopic stability as it moves down range. if it shoots well at 100 it has all the stability it needs for any distance.

Canadian 308 target rifles are usually 1:14 or 1:13. I have shot 180 match bullets with both, which are quite long. Conventional 180 gr hunting bullets are shorter and will shoot just fine in a 1:13.
 
GANDERITE said:
A bullet gains gyroscopic stability as it moves down range. if it shoots well at 100 it has all the stability it needs for any distance
Click to expand...

This is usually the case, but not always necessarily true. Velocity figures in a bullet's stability at a given twist rate as well, therefore a bullet that starts out stabilized may lose it's stability as velocity drops. I have proven this with a 10" twist 6.5 mm barrel where the long 140 match bullets were stable till about 400 meters and then lost their stability. The 264 Win Mag case gave them enough velocity and as long as sufficient velocity remained, they would be OK, but somewhere on the far side of 400, they would start to yaw and create keyholes in the target. I saw similar results in a 257 Roberts with the 120 grain bullet and a 12 twist barrel. Regards, Eagleye.
 
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