Surface temperature of projectiles

How hot could that lead bullet be at impact time? There is a trivial upper bound, that the temperature of the bullet must be lower than the melting point of lead³⁵, $327.4\tccentigrade$ at 1 atm, because the recovered lead bullet did not deform badly. The actual surface temperature of the bullet at impact time must be significantly lower than this upper bound, as explained below.

• In [MSW], the authors examined a 9-mm Lugar bullet in flight, at a muzzle velocity of approximately $350$ m/sec, with infrared thermography. The surface temperature of such a bullet was reported to be $147$- $152\tccentigrade$.

• In [SK, p. 185], the authors pointed out that only the surface of the bullet is hot, while the core remains cold.

  ``The thermal conduction being a rather slow process and the projectile motion taking place within less than a second, the generation of heat is limited to the top layer of the projectile and thus the core remain unaffected.''

  They also cited [LM] for a theoretical estimate of temperature increase on the surface of a bullet. The results, for the $7.62\times51$ mm NATO projectile³⁶, are: $160\tccentigrade$ inside the barrel, and at most $55\tccentigrade$ due to friction with the air. So the absolute maximum surface temperature of the said NATO projectile can reach, from a room temperature of $30\tccentigrade$, is approximately $245\tccentigrade$.