Max bullet speed

Dirk Bruere at NeoPax

A future gun physics question.
Simply stated, what is the maximum practical speed of a bullet in air at
(roughly) sea level? Ignore the acceleration mechanism.

I assume that it is the point at which the bullet melts and deforms due
to air friction. If we assume (say) a tungsten projectile and a temp of
3000 degC approx then what would be the corresponding initial velocity?

Dirk

Uncle Al

Dirk Bruere at NeoPax wrote:
>
> A future gun physics question.
> Simply stated, what is the maximum practical speed of a bullet in air at
> (roughly) sea level? Ignore the acceleration mechanism.
>
> I assume that it is the point at which the bullet melts and deforms due
> to air friction. If we assume (say) a tungsten projectile and a temp of
> 3000 degC approx then what would be the corresponding initial velocity?

You may get compressive failure before you get melting. Tungsten
happily burns in air. Tantalum carbide has 500 C better temperature
performance and high strength without sacrificing much density.

"Blunt body" designs form a thick shockwave ahead of the body that
both deflects the heat and rapidly decelerates over distance. If you
are really zooming along, an ultrahypersonic body passes through its
own mass before flashing into plasma.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf

Dirk Bruere at NeoPax

Uncle Al wrote:
> Dirk Bruere at NeoPax wrote:
>> A future gun physics question.
>> Simply stated, what is the maximum practical speed of a bullet in air at
>> (roughly) sea level? Ignore the acceleration mechanism.
>>
>> I assume that it is the point at which the bullet melts and deforms due
>> to air friction. If we assume (say) a tungsten projectile and a temp of
>> 3000 degC approx then what would be the corresponding initial velocity?
>
> You may get compressive failure before you get melting. Tungsten
> happily burns in air. Tantalum carbide has 500 C better temperature
> performance and high strength without sacrificing much density.

The material is really only peripherally relevant to the question. So
we'll assume Tantalum Carbide.

> "Blunt body" designs form a thick shockwave ahead of the body that
> both deflects the heat and rapidly decelerates over distance. If you
> are really zooming along, an ultrahypersonic body passes through its
> own mass before flashing into plasma.

I'd forgotten about supercavitation...
Anyway, any ideas on speed?

FFF
Dirk

Ken S. Tucker

Dirk Bruere at NeoPax wrote:
> Uncle Al wrote:
> > Dirk Bruere at NeoPax wrote:
> >> A future gun physics question.
> >> Simply stated, what is the maximum practical speed of a bullet in air at
> >> (roughly) sea level? Ignore the acceleration mechanism.
> >>
> >> I assume that it is the point at which the bullet melts and deforms due
> >> to air friction. If we assume (say) a tungsten projectile and a temp of
> >> 3000 degC approx then what would be the corresponding initial velocity?
> >
> > You may get compressive failure before you get melting. Tungsten
> > happily burns in air. Tantalum carbide has 500 C better temperature
> > performance and high strength without sacrificing much density.
>
> The material is really only peripherally relevant to the question. So
> we'll assume Tantalum Carbide.

I think the physical limit is explained here...

http://en.wikipedia.org/wiki/Cherenkov-Vavilov_effect

otherwise we'll need a precise definition of the
"bullet" you have in mind.
Regards
KST