hypersonic
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- Dec 12, 2005
- Messages
- 169
Nope way slower than that LOL
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220 Swift, twist rate, barrel length
- Thread starter buda
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Nope way slower than that LOL
jjmp
Well-Known Member
Mikecr, thks for coming back and explaining that ! I was to quick to judge my bad, I guess it won't be the last time twist can be or get confused . Regards and Happy New Year Everyone!!! jjmp
Mikecr
Well-Known Member
I wanted to add a point about choice in stability.
There are stability calculators out there that provide stability(Sg) numbers for you like 1.0 (just stable) -1.3 (marginally stable) -1.5 (fully stable).
In load developments I've seen twice where marginal stability shot worse. In both cases shifting to a shorter/higher stability bullet(of the same weights) greatly improved grouping.
My range is at sea level +/-2' depending on tide. My measure of air density conditions is calibrated per metrology lab at work, and my software is really good.
I've watched stability as a dominant change, have a bigger affect than I thought it would.
Bryan Litz(Berger) recommends at least Sg 1.5, and I'm compelled to agree all the way.
I really don't believe that over-spinning bullets (within reason) will have a worse affect than marginal stability or worse.
Sg climbs as the bullet slows downrange (before transonic) to the point that a 105VLD leaving the muzzle at 3Kfps and Sg 1.5 will climb to Sg 4.5 by 1kyds. This doesn't hurt a thing. Right?
But if you don't have enough spin to cover muzzle release well(biggest disturbance), downrange stability is too late anyway. The damage is already done.
There are stability calculators out there that provide stability(Sg) numbers for you like 1.0 (just stable) -1.3 (marginally stable) -1.5 (fully stable).
In load developments I've seen twice where marginal stability shot worse. In both cases shifting to a shorter/higher stability bullet(of the same weights) greatly improved grouping.
My range is at sea level +/-2' depending on tide. My measure of air density conditions is calibrated per metrology lab at work, and my software is really good.
I've watched stability as a dominant change, have a bigger affect than I thought it would.
Bryan Litz(Berger) recommends at least Sg 1.5, and I'm compelled to agree all the way.
I really don't believe that over-spinning bullets (within reason) will have a worse affect than marginal stability or worse.
Sg climbs as the bullet slows downrange (before transonic) to the point that a 105VLD leaving the muzzle at 3Kfps and Sg 1.5 will climb to Sg 4.5 by 1kyds. This doesn't hurt a thing. Right?
But if you don't have enough spin to cover muzzle release well(biggest disturbance), downrange stability is too late anyway. The damage is already done.
RD57
Well-Known Member
My 220 is a Wilson Arrow 14 twist and it shoots the Varmageddon Tipped and Berger FB Target 55's with outstanding accuracy. It shoots these in the .4" - .5" groups at 200 yards. Using a couple of stability calculators on-line indicates that they are marginally stable but my rifle disagrees.
It's interesting to me that the British commonwealth fullbore competitor's 30 inch barrels shooting 7.62 NATO M80 ball ammo with 147 grain FMJBT bullets at 1000 yard targets leaving about 3000 fps often got best accuracy with 1:14" twist rifling.
Mikecr
Well-Known Member
This thread is about 22cal
My 220 swift is a 16 twist 26" barrel and I shot from 35gr to 55gr bullets, when it was shot out I turned it into an Ackley Improved. The heaviest I can shoot now are those 69gr Sierra's HP's the ones with the short bearing surface.
Dean
Dean
