why Soviet frogman rifle shorter range in deeper water?

and why never featured in James Bond films? (also pistol version)

APS underwater rifle - Wikipedia https://en.wikipedia.org/wiki/APS_underwater_rifle

I always felt that water resistance under great pressure would be nearly same as sea level, since pressure is all directions.

Maybe to do with effect of pressure on initial cartridge expansion/explosion? Maybe effects of pressure on CAVITATION around fast moving underwater object?

 

The resistance of an object to move in a fluid depends on viscosity. The viscosity of water is both a function of pressure and temperature.
Water - Absolute or Dynamic Viscosity https://www.engineeringtoolbox.com/absolute-dynamic-viscosity-water-d_575.html

 

IMO, the story goes like this - the two most important things to consider are:

1) what drives the projectile is the cartridge gas pressure on the rear. This pressure depends on the propellant in the cartridge and is mostly independent of the outside environment.
2) what opposes resistance is the water in front of the projectile (pressure) and on the sides of it (friction). The pressure depends on the depth, while the friction does not. Hence, the overall resistance is dependent on the water depth (increasing static or ambient pressure).​

So, while the projectile travels through the barrel it has the expanding gas behind it and the water pressure in front of it. The former one doesn't change with the depth, the latter one increases with the depth. The net result: the projectile accelerates less as the depth increses, and exits the barrel with lower velocity. Lower initial velocity means lower effective range.

 

For all common purposes, the water viscosity depends mainly on the temperature. The pressure required to change the viscosity by some non-academic percentage is of the order of 1000 atm (100 MPa) and more, which corresponds to a water depth of 1000+ meters.

 

I reckon it's the last one, changes in the cavitation envelope which would collapse sooner and at a higher velocity as depth increased. This would upset the projectile's stability, causing it to tumble.

 

Got to correct you there, Slavi; 1 atm~10m of aqua, which means 1000 atm ~10.000 m.
And both the limited acceleration in the barrel and the reduced cavitation bubble (=increased friction) during the travel outside the barrel will shorten the range.

 

Ups, you're right.

I am not quite sure about the direct influence (via static pressure) of the water depth on the size of the cavitation bubble in this case. IMO, the cavitation bubble behind a very-high-speed, cut-off body like this is comparatively much more dependent on the velocity of the projectile than on the water depth, in the range of depths (0-40 m) of interest here.
Since the projectile deceleration is a quadratic function of the speed, most of the action happens in the first few meters after the exit from the barrel, where the speed is highest. Therefore, I would expect the initial speed (at the exit from the barrel) to be the major player in this case, and that the depth acts via the initial speed much more than via the compression of the cavitation bubble.

But that's just my intuitive thought, and we all know that sometimes hydrodynamics can play cruel games with the intuition.

 

I agree. The graph shows that clearly.

 

graph ....... and common sense.

 

Mythbusters testing ammo travel in the water by shooting from above, at an angle . . . .

Short version ↓​

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Long version ↓​

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And below some underwater firing, with arms and ammo intended for above water use . . . .

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That's just an empty cry, could you explain your common sense in this regard . . ?

 

Hey TANSL, often you try to degenerate some other ones post with an contentless meaningless empty cry, then when asked about this behavior you don't reply, so you miss the chance to put up some content to the random drivel you posted on this thread . . .

Why is this . . ? - - - Do you lack the common sense you have preached there . . ?

 

There is a type of needle bullet, banned from warfare as being too mean and dangerous, called a lancet I believe. One reason for being banned was it's ability to penetrate between the weaves of bullet proof vests. It is a multiple projectile bullet, like a shotgun's pellets but with needles that flew straight. I'm not sure it outright killed so much as filled a person full of needles and made life very uncomfortable until they did die. Possibly they were non metallic and un x-ray able, so surgical removable was very difficult. It would seem such a long, narrow, needle like bullet might have better range than regular bullets underwater.

 

And in fact, the underwater bullets of the APS gun are steel needles:
The APS Russia’s Underwater Assault Rifle http://www.guns.com/2013/07/08/the-aps-russias-underwater-assault-rifle-what-frogmen-bring-to-pool-parties/

 

Never knew there's so much stuff to show off at pool parties . .

Underwater firearm - Wikipedia