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Nolo84 — .220 Zenith
Published: 2012-10-11 12:45:06 +0000 UTC; Views: 766; Favourites: 4; Downloads: 4
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Description
-.22 caliber-7.62x36/.220 Russian parent case
-With 55gr bullets: 1,050 m/s (20" bbl); 920 m/s (12" bbl)
-With 62gr bullets: 1000 m/s (20" bbl)
-With 77gr monometal bullets: 870 m/s (20" bbl)
-With 90gr bullets: 820 m/s (20" bbl)
-Fits within micro-length actions and AR-15 magazine wells (2.26" OAL)
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Comments: 13
Small caliber high velocity rounds are pretty sexy.
Especially since a BC of 0.5 comes in under 6 grams.
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I got a G7 BC of .285 for a 90gr bullet that could fit in this cartridge, which is roughly equivalent to a G1 BC of .580.
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Well, poorly designed it's 0.5 in 6 grams.
The only issue I've found with them (especially when shooting saboted them through a 10mm bore) is that they require a very tight rifling pattern compared to most other loads.
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The British IW or L64/65 had a 1 in 5" rate.
How much of an issue would it be to shoot a bullet that would normally go in a 1 in 8" barrel through a 1 in 5"/6"? I know it wouldn't really work the other way around.
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It would be overspun and at long range the angle of attack of the bullet would not line up with the trajectory, but for emergency use, you wouldn't notice a difference.
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I'm not sure whether it's that much of a deal. Under stabilizing is much easier than the other way around, so I suppose you'd be fairly okay.
Nevertheless, I've changed some things to that sets loads do fine with a common twist rate.
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Only at long range would you see any difference.
Also, overspun bullets generally have poorer terminal effectiveness.
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Isn't the lack of terminal effectiveness caused by the increased air resistance (and in turn, lower terminal velocity)?
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No. Overstabilized projectiles will yaw later and less often than ones that are stabilized just enough.
There was a marked difference in the terminal effectiveness of the early .222 Remington Special when shot through 1-in-14 twist barrels versus later M193 out of 1-in-12 barrels.
It is also my understanding that the Swedes find their version of SS109 to have better terminal effectiveness through their AK5 rifles than through an M16A2. Why? AK5s have a 1-in-9 twist barrel, whereas M16A2s have 1-in-7 twist barrels.
Certainly, the misalignment of the procession of the bullet will increase drag and thus the projectile will strike at long range with less velocity (but a higher angle of attack, which, paradoxically, probably induces yawing earlier), but the examinations of M193 through 1-in-14 and 1-in-12 barrels was all done at the muzzle, where the mismatched procession would not be evident.
Does that answer your question?
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Well, all of it makes sense, its just a matter of which makes slightly more sense.
Sadly, terminal ballistics isn't a subject taught at the HVA. It'd beat the hell out of material & substance sciences.
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It's also possible that the overspun bullet is so stabilized that even though it will hit a target at long range at a high angle of attack, it won't yaw early due to its stability.
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