rafter3c wrote on Dec 16
th, 2014 at 12:19pm:
Jack,
Thanks for your informative reply. Wanting to add the .338" barrel and looking for the best all around twist rate. I have talked with, I am sure, a mutual friend of ours on this subject. Your post fit right in. I feel the 245gr. lead bullet is a good fit for the 33-47 but getting the shooters what they want and what will work best is the question. I think the 1-16 gives me a bit more MV and less recoil than the 1-14. So far the 1-15 seems to be the best solution. I will go in the shop next thursady and talk with Al in regards to finishing 10 more, on the last run of, Borchardt actions and adding the 33cal. barrel. I would like to hear your thoughts on the subject. Ken Lewis
Hi Ken,
The rule-of-thumb is to choose the slowest twist rate that will achieve gyroscopic stability at the muzzle. Faster twist rates actually exacerbate the effects of imperfections in bullets, rifling, and crown.
As the bullet moves through the barrel, it is constrained to rotate about the "center of form." When the bullet exits the muzzle, it then rotates about the "center of mass." If the bullet is perfectly balanced, the center of mass will lie on the center of form.
However, if the bullet is out of balance (due to internal defects or uneven rifling) the center of mass will
not lie on the center of form and the bullet will physically jump off-axis when it leaves the muzzle. The faster the bullet is rotating, the greater the jump.
This "jump" increases initial dynamic instability. Among other things, greater initial dynamic instability degrades the "effective" ballistic coefficient of the bullet which, in turn, increases lag time between muzzle and target. As lag time increases, the effect of wind on the bullet increases.
So, that's the theory. I'm not a barrel maker and I've never owned a .33 caliber rifle so I have no practical experience to draw on.
JackHughs
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