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12/23/2013 9:07:14 AM EDT
I often wonder... If we're supposed to get close to the lands for accuracy (small-no jump), why do barrel manufacturers cut the chambers so deep? Why not cut them to mag length dimensions? The ojives on pretty much all bullets would be roughly in the same place with mag length loads. It just seems like the jump between mag length bullets and the lands on most ARs is way more than it needs to be.
12/23/2013 9:36:23 AM EDT
[#1]
Quoted:
I often wonder... If we're supposed to get close to the lands for accuracy (small-no jump), why do barrel manufacturers cut the chambers so deep? Why not cut them to mag length dimensions? The ojives on pretty much all bullets would be roughly in the same place with mag length loads. It just seems like the jump between mag length bullets and the lands on most ARs is way more than it needs to be.
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I am no expert but let me say that some of the heavy bullets dont even fit in a mag. Those bullets would be unusable in such a short chamber.
12/23/2013 9:48:56 AM EDT
[#2]
Quoted:
I often wonder... If we're supposed to get close to the lands for accuracy (small-no jump), ...
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Who says we're "supposed to"?  Most bullets tolerate jump just fine.  The ones that don't, and that are generally loaded long to get close to the lands, can't be loaded to mag length anyway.
12/23/2013 10:09:40 AM EDT
[#3]
Quoted:
I often wonder... If we're supposed to get close to the lands for accuracy (small-no jump), why do barrel manufacturers cut the chambers so deep? Why not cut them to mag length dimensions? The ojives on pretty much all bullets would be roughly in the same place with mag length loads. It just seems like the jump between mag length bullets and the lands on most ARs is way more than it needs to be.
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It's called "Pressure" and the less the jump the higher the pressure.  Rifle and ammo manufacturers need to make sure that all ammo is safe in all rifles, giving the bullet a jump is one of the ways they accomplish this.

That said, loading up close and personal to the lands is NOT always the best place for accuracy and is often times not even close to the best OAL.  Every rifle is different and to claim that all or even most rifle shoot better up against the lands is simply not true.

Here is a study by Barnes on OAL vs Accuracy vs Pressure.  Note that there was more than one OAL sweet spot in their tests.  One up close and another Waaay far away.

http://www.barnesbullets.com/resources/newsletters/september-2007-barnes-bullet-n/
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