Topic of the Month: May
2002
Some Comments on Shooting
Underwater
What would happen if someone fired a
rifle underwater? Would the pressure produced rupture the gun? It is assumed under these
conditions that the barrel and action are completely submerged and the barrel is full of
water.
To get an answer to this question the NRA
performed a number of underwater experiments. In the first experiment the bullet and
powder charge were removed from a .45 ACP cartridge and the primer flash hole was covered
with a waterproof disk to keep water out of the primer. The gun was loaded with the primed
cartridge and held vertically while the barrel was filled with water. Without changing the
gun position the gun was fired. There was the sound of a mild ‘splat’ as the
water was blown up against the ceiling. The gun was not damaged.
Next the gun was loaded with another primed
cartridge and the fully submerged gun was fired. No noise could be heard, but a spurt of
black water was ejected from the muzzle of the gun for a distance of about one-foot.
Reassured that the gun mechanism would work underwater, the gun was loaded with a Service
ball cartridge and fastened in a heavy vice on the bottom of a tank. The tank measured
40"x24"x24" and was filled with water. Care was taken that the barrel was
filled with water and had no air pockets. On firing (by remote control) there was a lot of
disturbance and quite a bit of water splashed out of the tank. The bullet passed through
16" of water, a 7/8" pine board, 6" more of water and finally came to rest
against a second board after making a deep dent in it. The empty cartridge was not
ejected, but jammed with the pistol slide part way open and the cartridge caught in the
ejection port. The pistol was not damaged in any way.
The experiment was continued with a
.30-’06 Model 1903A3 Service rifle with the stock removed. The rifle was clamped in a
vice on the bottom of a tank and loaded with an M2 Service round containing a 152-gr.
bullet. Since there was only 6" of space between the muzzle and the inside of the
tank no attempt was made to place anything inside the tank to measure penetration.
However, four soft pine boards 7/8" thick were placed outside the end of the tank and
in line with the rifle barrel.
When the gun was fired (by remote control)
the bullet penetrated 6" of water, the 3/64" steel tank wall, all four boards
and lodged in a solid oak plank used as a backstop. The bolt could not be opened by hand,
but opened easily to a few light taps with a rawhide hammer.
The cartridge case, just in front of the
cannelure had expanded by about .032 inches and the primer pocket had opened up from the
standard .209-inches to .228-inches. The primer was punctured and a small quantity of
black smoke was observed to escape from the surface of the water, near the breech, when
the gun was fired. The case and primer pocket expansion was greater than those usually
seen when a 70,000 p.s.i. high pressure test load is fired from the same type of gun, so
the pressure was probably much higher than the 70,000 p.s.i.
The rifle bore, full of water, would
contain about 385 grs. of water, which is equivalent to adding 2.5 times the normal bullet
mass that the powder pressure has to move. In spite of this additional resistance from the
water, the rifle showed no bulging of the barrel or other damage.
While this limited test is interesting and
gives you some idea what may happen it is not definitive. The results could be different
if the same test were performed with a higher intensity cartridge or one of the magnum
cartridges with large case capacity.
Watch our web site for the next
month’s topic of interest. Until then, shoot safely and know where you bullets are
going.
Sincerely,
The Ballistician
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