Tuesday, June 26, 2012

.50BMG vs Rubber fuel Tanks

Ever wonder why vehicles aren’t more susceptible to fire from a few stray rounds of .50 BMG?  Surely a couple of .50s will have fuel spraying around everywhere looking for an ignition point.

The answer is self-sealing fuel tanks.  The tanks are a rubber/fabric composite and insoluble to the fuel used, except for one layer which swells when exposed to gasoline or other fuels.  The swelling polymer plugs the hole.  The next question is how fast do they seal?  Again having even a little fuel spraying around a hot engine is a formula for disaster.

I found this video at www.robbietanks.com/multimedia/videos.  Select the one called .50 cal tumbled Robertson Improved HMMWV Tank or Improved LAV Tank.  What I think is really cool is the bullet exits the tank backwards and sideways.

I expected the .50 to just drill its way through the tank and exit point first.  A .50 cal BMG leaving sideways…  Talk about wound channel!!!

As I thought about it, I guess it makes sense.  Traveling blunt end first, the bullet makes a shock wave expanding the material away from the bullet’s leading edge.  The point acts as a trailing edge to stabilize the motion.  Kind of like the pre-shuttle, onetime-use space capsules on reentry.  

I wonder if my .223 boat tail would duplicate that motion?  It probably doesn’t have the mass, and therefore energy to keep plowing through material until some form of equilibrium stability is achieved.
Of course, the bullet may just tumble without any rhyme or reason and it was just caught that way on tape.

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