From: [EMAIL PROTECTED]
Hi there,
here's my tuppence worth.
Andrew, you should know better than to say pressure has
no effect on melting point! At the kinds of pressure and
temperature, and time scales, involved in firing a bullet,
you will get melting of a lead surface, simply because
the lead has too low a thermal conductivity to transmit
the heat away, over the time scales of a few microseconds.
You will see no evidence of melting, since the lead in the
bullet was melted after it was put in there, so there
will be no change to the crystal structure of the metal,
and besides, you would have to examine the very surface
of the back of the bullet to see anything. The melting
happens, but whether it affects accuracy is another matter.
As for lead flowing under extreme pressure, this is also
sure to happen, as the forces on a bullet are enormous,
acceleration wise, and the ductile strength of lead is
very low. Just the level of spin, and the resulting
centripital acceleration will distort something soft. That
this distortion is high enough for the gas seal to occur
effectively or whether the accuracy is affected is really
down to the initial pressure peak, rather than the
temperature, etc.
As for the lack of lead in the barrel, you would get an
impressively thin layer of deposited lead, which would
appear as the gunge you push out the barrel with Hoppes
and a rod. It would be disturbed every shot, and would be
mixed with all the unburned powder, etc.
As for baked alaska, the merangue around the sides and
the sponge under the icecream offer insulation for the
short cooking time. This means very little heat is
transferred to the icecream, as it is air currents only,
and air has a very much lower thermal capacity than icecream.
If you look at the top, it has melted. I suspect that the
bullet will also have just that surface melting, with the
sides protected by the barrel and/or the jacket.
Of course, all this is moot, since you are both talking
pples and pears, as a jacketed bullet and a lead bullet
are totally different in their reactions. I suspect that
Steve/Rob are wrong, as the level of melting would
be tiny in a jacketed round. However, there is another
reason for the greater stabilty of open based jacket
rounds. As the bullet spins up, any density variation in
the core will be spun out, and the level of imbalance
will drop, and any tiny air gaps will be forced out. A
few milliseconds later, the bullet will stabilise fully,
then impact the target a few moments later. Having an
open back means the lead will be rammed forward into the
jacket even better.
Presumably, this idea falls down if you look at a semi
jacketed bullet with an open back. Having said that, I
don't think I have ever seen one, but the pistol ban
means I never had my own, so never played so much. I am
willing to be corrected, but the lead would blow straight
through the middle of the jacket without some form of
crimp or partition.
Nigel
Send your details to ShootersWeb.co.uk to be listed on
(hopefully) the UK's most complete online listing of clubs
and ranges.
--
I think it depends on the pressure, 9x25 Dillon has to be
one of the highest pressure pistol rounds there is.
Steve.
Cybershooters website: http://www.cybershooters.org
List admin: [EMAIL PROTECTED]
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