I think you’re incorrect here. The latest NATO SS109 5.56mm round is actually more stable than the previous M193 was…
Right, to clear up this twist business.
The older, 55 grain M193 ammunition was used in rifles with a 1:12" twist barrel. This barrel will not stabilise the 62 grain SS109 or heavier bullets. This is because these bullets are longer (the weight of the bullet is usually used as a proxy for this), and require a 1:9" or tighter twist. The NATO standard is actually 1:7" to adequately stabilise tracer, which is even longer.
You can, however, fire lighter bullets through the tighter twist barrels.
Therefore, the M16A1 can only fire M193 through its 1:12 barrel, whereas the M16 A2 can fire either M193 or M855 (SS 109).
Is stability an aerodynamic or gyroscopic issue?
Wouldn’t there be elements of both, depending upon conditions?
If a projectile had its nose sliced off at an angle, I assume it’d be less stable, partly because of the way it attacked the air and partly because of the off-centre weight.
My recollection of artillery on Kokoda in New Guinea in WWII is that they had to correct for humidity at different times of day, which is purely aerodynamic.
From memory that’s a simple density issue though - higher humidity gives higher air density, which in turn gives higher dynamic pressure on the front of the shell and so higher drag.
Reason I’m asking is that if it’s a gyroscopic issue then length is irrelevant and it’s purely down to weight, while if length does come into it it has to be aerodynamic - at which point things potentially get really rather interesting.
Some people found this out the hard way when there was unfortunately still a small number of M-16A1s in the mix during the first Gulf War. The logistical problems are obvious, though the green typed bullets were a big clue to a soldier that payed attention. In fact I had an A1 assigned to me in my Reserve spot up until the late 1990s!
Now if they would convert everything to the M-16A3 standard (the M-16A2 with the cyclic feature in place of the three-round-burst for the US Navy SEALs), we’d be okay…
I’ve also been told that the M193 5.56mm bullet didn’t so much as “tumble” as it exploded inside the human body at close ranges.:shock: Any comments on this?
It is an interesting combination of aerodynamics and gyroscopic effects – in a vacuum we wouldn’t need to worry about spin stabilisation anyway.
The M193 can split at the cannelure at close range, fragmenting. It doesn’t “explode”. The SS 109 does this as well, by the way. another thing the M193 did was tumble on contact with light foliage and hit people beam on, which was also nasty.
Well, up to a point. Unless you were going for squeeze-bore stuff however you probably would have to have some spin on it though - two circles will only touch at one point, which isn’t great for accuracy as you can’t tell where that point will be. Spinning it at least means you have a little more control over that point. IIRC this is a (minor) issue with APFSDS.
Okay, hypothetical, since we are not actually firing projectiles in a vacuum, all you need to do is provide a small interference fit. then it will touch around the whole circumference!