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Old 03-15-2006, 08:58   #32
Gene Econ
Quiet Professional
 
Join Date: Jul 2005
Location: Lacey Washington
Posts: 737
Quote:
Originally Posted by MAB32
Gene, When 62 grain first appeared on the gunshow circuit shortly thereafter I was told that I would be wasting my money if I bought it because the 1-12 twist rate would not be able to stabilize the round enough to be accurate and I would end up with mostly "keyholing" at distances greater than 100 yards. I never experienced it and got acceptable accuracy to boot. Then I purchased an A2 and tried the direct opposite; 55 grain through it and was again told, "your're wasting your money becuase the twist rate is too fast for 55 grain and it will rip off the jacket as it goes through the bore and on on and so forth and so with. Never had a problem with shooting the 55 and it made nice small holes at 100 yards too. Did anybody else hear this and was it just "hype" or is there some merit to it?
MAB:

Basically, your 12 turn twist really needs a short and relatively light 5.56 bullet. 55 grains is about it. You can shoot the 62 gran stuff out of it but it will yaw and pitch too much for good accuracy. I doubt it will tumble unless you go past 300 yards but your shot groups will be very poor.

It is better to overstabalize than understabalize so firing the 55 grain stuff out of the 1/7 barrels on the A-2 is just fine -- to a point. I wouldn't expect as good accuracy from them past 300 yards as I would a heaiver and longer bullet.

You need to research 'precssion' and 'nutation' in some good ballistics books. If you want, also research the relationship between the center of mass and point of pressure on bullets. They tie together.

As for in bore jacket failure -- I haven't seen it happen in bore. I have seen bullets literally explode in flight due to too fast a spin plus too fast a velocity. Match grade or varmint bullets use pretty thin jackets and if you spin them too fast -- normally too high a velocity -- they may have a jacket failure in flight. You see a puff of grey as the bullet disintegrates. It doesn't happen in bore unless the jacket was defective in some manner.

Military ball uses very thick jackets. For hunters, they would almost be considered 'solids'. You won't see a jacket fail in flight on one of these from any commercial or issued rifle.

Gene
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