What is the difference between a 1:7 twist and a 1:9 twist? Besides for the obvious of one having a full twist in 7" and one in 9". I mean, what are the advantages/disadvantages? Does it effect the bullet?
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The faster the rifling twist is, the longer the bullet that it can stabilize.
Longer bullets need more rotational velocity to be gyroscopically stable than shorter ones. Since for a given caliber bore diameter is fixed, longer bullets are proportionally heavier than shorter ones.
Hence common perception is that faster twist barrels are necessary for stabilizing heavier bullets. While that is generally true when speaking of lead cored, copper jacketed bullets, all-copper bullets (like the Barnes-X bullet) are different.
For example, a 1/9 20" barrel is sufficient to stabilize a 70 grain lead/copper bullet in .224" diameter. But an all copper bullet of the same weight HAS to be longer and thus will most likely keyhole out of the same barrel at a similar muzzle velocity. So all copper bullets need faster twists than lead cored bullets of the same weight.
Obviously long bullets that don't have a fast enough twist aren't as stable or stable enough. What happens if the shorter bullet is spun faster than ... "normal" I guess?
Obviously long bullets that don't have a fast enough twist aren't as stable or stable enough. What happens if the shorter bullet is spun faster than ... "normal" I guess? Are you better off getting a 1:7 barrel even if you won't usually be shooting long bullets, but may shoot them every once in a while?
I have shot LOTS of 45 grain WW White Box ammo at the 200 yard line for offhand and stitting practice in Highpower Rifle and I never lost one when shot through a 1/7 barrel.
So yes. Get the fastest rifling rate you can find. It simply gives you more options.