Re: Odd-ball conversions and left field questions

[Mike Fortey <forteymj@xxxxxxxxxxx>]

> My point was that concidering the construction of
> almost all firearms, built
> to withstand the rigors of use and combat.  That any
> void in the frame would
> be more than capable of containing 14psi

I would probably think so too, but it's kind of worth
checking, before you take it into vacuum, isn't it?

, a shaken
> soda can is under more
> pressure. 

Remind me to take a can of shaken Pepsi to 30 feet
some time so I can check that out =P.

> I would postulate that even the weakest
> frame would contain 5 atm
> (~70 psi), normal military weapons would be much
> higher, 10+ ATM, maybe.

I don't think that I'd go that far. Well, maybe the
frame itself, but there are lots of other pieces that
need to be lacking voids too. 10 ATM is a lot of
pressure. Remember that a lot of plastic is featured
in today's weapons. Again, I would certainly want to
check the weapon and maybe drill some vent holes in
it. I'd also want holes drilled in any near-void
areas, so as not to cause slower pressure
equalisation.

  A
> shaken soda can is under more pressure.

10 ATM? Remind me to take it to 300feet! I would be
very, very surprised if the top of the can (containing
the gas - you can't squash liquids to any real extent
without silly pressures, which is why high end diving
watches are liquid filled) didn't buckle. =)

> Exactly, the weakest point in a cartridge is the
> seal between the bullet and
> the case and the bullet is usually seated with 20-40
> pounds of pressure on
> the loading press.  

Which means that it's actually quite close to popping
itself off in a vacuum already, yes? Within 100% of
doing so in most cases? 

> With the
> pressures that a cartridge case is designed for, 14
> psi is insignificant
> ~0.01% chamber pressure.

Err, yes...assuming that it's supported by the chamber
and that you want the bullet to pop out the end. What
happens if it's in the magazine and the bullet falls
out of the end? What if the cap pops off your
hollowpoint? Again, I'd want my rounds checked before
taking them into a vacuum, and seated a little tighter
than normal.

> The differance of 1 ATM would be to small for the
> mechanism to notice.  The
> bolt might take a little more abuse on a gas
> operated weapon, but nothing to
> cause an imediate malfunction, just shorten it's
> life a little, rattle
> something loose sooner, nothing general maintenance
> wouldn't fix.

Well, I'm not claiming to know much about it, but...

Normally a gas operated weapon relies on the
overpressure behind the round to work the action. In
addition to that gas working the action, a proportion
of the gas is also being vented out of the action. In
a vacuum, that proportion of the gas would be activly
'sucked' out. Would that reduce the amount of
overpressured gas travelling down the barrel, meaning
that the user would have to switch to 'M' on the gas
tube...would even that be enough? Alternatly, would
the reduction of air-pressure resistance on the action
take things the other way?

My thinking as to GDW's comment that 'caseless ammo
doesn't work in vacuum' is probably that they 'phoned
up H&K and asked 'will the G-11 work in a vacuum?',
and H&K replied 'no' for some reason specific to the
G-11. *shrug*. Something that it occured to me that
we've not really addressed is the temperature. Vacumm
of course does mean that heat is not actually
conducted very well at all, but I'd be interested to
see how some modern materials used in firearms hold up
to the cold. Maybe that's the reason that the G-11
wouldn't function in space? The composition of the
rounds might suffer and either not ignite or perhaps
even flake away into powder?

As I commented in my original post, modern firearms
(given the correct lubrication) will indeed
theoretically work in 'space'. It's also worth
exposing any weapon you planned on taking to a few
sudden pressure changes and shock tests to make sure
that that weapon will be ok - checking for obvious
weak void spaces, well seating the rounds and drilling
vent holes in any suspect areas. A fire-fight in a
vacuum is about the last enviroment imaginable where I
personally would be happy about having
non-tested-to-stupid-standards kit. 

Mike







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