| From: | Paul J. Adam Paul@********.demon.co.uk |
|---|---|
| Subject: | exchange rates, and APDS...pronounced APP-ee-das ? : ) |
| Date: | Wed, 24 Feb 1999 21:29:39 +0000 |
>As others have noted, APDS consists of a hardened metal core, surrounded by
>a softer jacket (for small arms this would probably be some type of plastic).
>When the bullet clears the muzzle of the gun, the jacket falls away (usually
>by means of air resistance) while the core travels onward. This gives the
>projectile a smaller cross-section, which means (1) reduced energy loss from
>air drag and (2) a more concentrated energy transfer at the point of impact.
Also, it means you get the best of both worlds. In the barrel (internal
ballistics), the round is large and light and thus easily accelerated to
a very high velocity. Outside, once the sabot is discarded, it's small
and dense and _keeps_ that velocity.
Here I digress into ammunition history :) Two earlier versions were
APCNR and HVAP.
HVAP was an aluminium projectile with a hardened steel or tungsten core:
it was halfway to APDS, in that it was a large light projectile that
reached a terrific muzzle velocity (High Velocity Armour Piercing) and
had good penetration from the subcalibre core; but the large, light
shell suffered relatively badly from air drag and wind, losing velocity
and range faster than a conventional projectile.
APCNR was "Armour Piercing, Composite, Non-Rigid": it was the last step
before APDS, and was used on the British two-pounder AT gun. It
resembled a HVAP round, with a subcalibre tungsten core in an aluminium
body that achieved high muzzle velocity, but at the muzzle a tapered
adapter swaged the 'skirted' aluminium body down to make the projectile
smaller and give it better external ballistics. The downside was that
the gun could _only_ then fire APCNR, no canister or HE, but 2pdr APCNR
was a great boon to British and Commonwealth tank crews and gunners in
the Western Desert.
The logical next step, of course, was to have the aluminium body fall
away rather than be swaged down, eliminating the awkward and inflexible
muzzle attachment and improving performance further... and so to APDS.
>The metal core is usually made out of either tungsten or depleted uranium
>(the waste product left over after purifying raw uranium to make reactor-
>grade or weapons-grade fuel, and composed 99.xxx% of U-238). Up until a few
>years ago, APDS tank rounds were made of DU, but most militaries have been
>switching over to tungsten, partly because tungsten costs less,
Overall. DU is basically free if you're a nuclear power, and also fairly
useless (although it's used for counterweights and ballast in aircraft)
The problem is, the raw material's cheaper (piles of it sitting around
any uranium seperation plant) but it's much more expensive to handle and
work with.
>and partly
>because tungsten is easier to machine. (DU is also pyrophoric, which means it
>gets real
>hot and creates sparks when it strikes metal, but how much that special effect
>adds to the round's combat effectiveness is subject to some debate.)
As a treadhead acquaintance said to me, "when your body's being
perforated by hypersonic chunks of metal, who cares if they're burning
or not?"
>Now that Paul Adam is back on the list, he can probably cover whatever holes
>I may have overlooked.
... which means I couldn't resist leaping in. Thanks for the kind words,
Jon :)
--
Paul J. Adam
