[geeks] Re: [rescue] OT: Stuffed Proliant?

[Kurt Huhn]

*Warning - long but educational.*

> When I played last, they rental guy (who was really into it) was talking
> about them penitrating steel rather easily.  Maybe he was just talking.
>

Total bullsh*t.  He was trying to seem more knowledgeable than he actually
was, and will end up looking like an ass.  Don't take this guy's advice on
anything...

>
> I thought the barrels had to be oversize because of the balls changing
> size with the weather?

Someone pointed out to me last night that a paintball wouldn't necessarily
expand when frozen.  They're partially correct - as I conducted an
experiment to find out what happens when you freeze paintballs..  Overall,
the paintballs didn't get bigger, but they did become horribly disfigured,
and not accurate past about 15 feet.  Several split apart in the barrel -
because their oblong shape created wierd tumbling in the barrel and they
scraped the sides excessively.

Different paintballs are different caliber - ranging from .678 to .689
normally, depending on manufacturer (other sizes do exist but are somewhat
rare).  Smart Parts makes a great barrel set (called 'Freak') with inserts
for the barrel that you can use to correctly match whatever brand/make of
paint you happen to be shooting that day.  Barrels also vary in bore size,
depending upon manufacturer and production run.  It's funny that way...

All in all, when playing paintball you have to try to match your barrel to
the size of the paint you're using.  Since you rarely have control of the
paint you'll be shooting, getting a good set of barrels is the only way to
ensure accuracy and range on commercial fields.

There are lots of articles out there on barrel and paint choices - the best
way to match your paint, though, is to place a paintball in the breech of
the barrel (off the gun).  It should slip down about half an inch, then blow
with a quick but not too firm puff.  The barrel should come out the other
end.  If the paintball drops out with you blowing, the paint is too small
for the barrel and you'll be wasting air and acuracy will suffer.  If the
paintball fails to exit after you attempt to blow it down the barrel, the
paint is most likely too big for your bore - and you could end up shooting
salad for most of the day.  Had this happen to me once - it ain't fun.

>
> >
> > Marbles from a paintball gun are an urban legend.  The diameter of a
marble
> > is far to small for the .68 caliber bore of a paintball gun's barrel.
That
> > means, poor air seal around the marble and a very low muzzle velocity -
> > somewhere around 175ft/sec according to the chrono in my garage (yes, I
> > tried it :).  Add to that, the friction of the glass material
>
> The way I understood it, they were marbles sized at the correct
> caliber.  I've never tried to find any, However.
>

Never seen any - I assume we're talking about the same marbles you can get
any toy/drug/hardware store.  Normally packaged in a mesh bag?  At any
rate - your paintball gun would need to be *heavily* modified, to the point
of being dangerous to even pull the trigger, to get the muzzle velocity
needed to expell a marble at sufficient velocity to pierce steel.

It's all simple physics.  Consider the surface area of a marble as it
impacts and buckles the steel.  The strength of the steel determines the
pressure needed to create a tear in the surface of the steel, and continue
it through to the other side.  Also, consider that a marble will shatter
simply by hurling them at a sidewalk - that action of shattering absorbs and
deflects all of the inertia and spreads it out over a *much* wider area.

Now - how fast would you need to make a marble move to pierce the steel skin
of a car?  I don't know... lets see...  A .22 has a muzzle velocity of about
1000fps, and carries about 84 joules of energy at the barrel (this is a 38
grain round).  Assuming this is the lower limit that can penetrate steel
(dunno for certain), we need to make a quick calculation.

::complicate calculations and some research....
1 paintball = 1.28 grams = .693 grains
using the muzzle velocity calculater at
http://www.arniesairsoft.co.uk/articles/fps_limits/fps_calc.htm
we find that a paintball traveling at 300fps carries 5.32 joules at the
barrel.  Ok, we know that isn't going to penetrate steel.  How fast would we
need to get it moving?  Let's try to get 84 joules, and totally disregard
the surface area of the impact...hmmm...1192 feet per second.  Obviously,
due to greater surface area of the paintball, we need get it moving faster
than that - but you get the picture.

So, try to crank up a paintball to fire at about 1200fps.  Not gonna
happen - never.  Even if we reduce the velocity by 30% allowing for bad
assumptions above (like actual energy needed being less) - you wouldn't ever
get a paintball gun to fire at 800fps.  Paintball guns would blow themselves
to pieces long before you got them to fire that high.

Now if we used a marble of average size, which equals 16mm and 18.5 grams.
That's a .64 caliber sphere.  Lessee....we need to make it reach 315fps at
the muzzel to reach 84 joules.  Sounds possible, right?  Wrong.  We need to
account for energy loss due to the projectile being undersized for the
barrel, and the increased force needed to accellerate the greater mass to
the necessary speed.....scribble...scribble...hmmm.....getting tired....

I'll leave it to you guys to figure out the ultra complex calculations,
assuming you care enough to do so.  At any rate, it's is a *very* safe
assumption that you'll never get a paintball gun (even heavily modified
ones) to fire a glass marble at speed sufficient to produce enough energy to
pierce the steel skin of a car (a car being the original example).

Shizen!  I haven't done this much math since high-shool!

>
> Maybe I'll have to try shooting stuff...... sounds like fun :-)
>

Shooting stuff is always fun!  I have an old plastic garbage can on the side
of my house that acts as a target when dialing in paintball guns after I
work  on them.  Last night I finished modifying a Tippmann Model 98 and went
out to dial it in.  It got cold enough to make the plastic brittle enough
that a 280fps paintball from 50 feet away put a nice clean hole in the side
of the garbage can facing me.  I thought it was so cool that I proceded to
put about 80 more nice clean holes in it :-)

Kurt
PS: attempting to move to Geeks...