Main Forums > The Roundtable

On RPG-7s

(1/4) > >>

Guest:
Thought I'd share a posting I just made on another board, just for the hell of it.


--- Quote ---It is my pleasure to prove you wrong.

Let us begin with listing the incorrect assumptions of Blueberet. In most of these, you can tell that he is applying a rudimentary understanding of ballistics incorrectly to the RPG-7 according to how he "thinks" it should work. I suspect that as a child he ate 'wall candy' or was dropped on his soft, undeveloped head repeatedly.

Firstly, he assumes that armor penetration is based on the relative velocity of the warhead.

Secondly, he assumes that the booster charge boosts the RPG warhead above it's normal velocity, because it is named a "booster". His train of thought is obviously that it is "boosting"- an understandable mistake if rather silly.
Once confronted with this he has invoked a mythical "extra" booster charge. Again, I will show how ridiculous this is.

Thirdly, the tedious fool denies that armor penetration of approximately two feet is possible from an RPG warhead.

My theory is that all of these misconceptions stem from a complete misunderstanding of how a RPG-7 warhead works, seeing as he is acting like it penetrates armor under the same physical laws as a .50 BMG or something. Either that or major brain damage that prevents his mind from processing logical thought.

Let's talk about how they work. There are three main types,
PG-7VL standard HEAT warhead for most vehicle and fortication targets, PG-7VR dual HEAT warhead for defeating modern heavily armored vehicles, TBG-7V thermobaric warhead for anti-personnel and urban warfare, OG-7V fragmentation warhead for anti-personnel warfare (within caliber due to limitations of international treaties).


--- Quote ---PG-7V:
Warhead: Single-stage HEAT
Round weight: 2.6 kg (5.7 lb)
Diameter: 70,5 mm (2.7")
Penetration: Over 330 mm RHA (12.9")

PG-7VL:
Warhead: Single-stage HEAT
Round weight: 2.6 kg (5.7 lb)
Diameter: 93 mm (3.65")
Penetration: Over 500 mm RHA (19.5")

PG-7VR:
Warhead: Tandem HEAT
Round weight: 4.5 kg (9.9 lb)
Diameter: 105 mm (4.1")
Penetration: Over 600 mm RHA after reactive armor (23.4")

OG-7V:
Warhead: Fragmentation
Round weight: 2 kg (4 lb)
Diameter: 40 mm (1.6")
Maximum kill area for personnel wearing body armor: 150 m (492 ft)

TBG-7V:
Warhead: Single-stage thermobaric
Round weight: 4.5 kg (9.9 lb)
Diameter: 105 mm (4.1")
Kill radius: 8 m (26 ft)
Penetration: From 150 to 480 mm RHA (6 to 18")I should not have to cover thermobaric or fragmentation. I will now focus on HEAT (High Explosive Anti-Tank), the penetration mechanism of the RPG. Note that I also underlined the PG-7VR. We will get to that later. I think that a simple quotation will work to explain how HEAT works:


--- Quote ---HEAT) rounds are made of an explosive shaped charge that uses the Neumann effect (a development of the Munroe effect) to create a very high-velocity jet of metal in a state of superplasticity that can punch through solid armor.

The jet moves at hypersonic speeds (up to 25 times the speed of sound) in solid material and therefore erodes exclusively in the contact area of jet and armor material. Spacing is critical, as the jet disintegrates and disperses after a relatively short distance, usually well under 2 metres. The jet material is formed by a cone of metal foil lining, usually copper, though tin foil was common during the Second World War.

The key to the effectiveness of a HEAT round is the diameter of the warhead. As the penetration continues through the armor, the width of the hole decreases leading to a characteristic "fist to finger" penetration, where the size of the eventual "finger" is based on the size of the original "fist". In general HEAT rounds can expect to penetrate armor of 150% to 250% of their width, although modern versions claim numbers as high as 700%.

HEAT rounds are less effective if they are spinning, the normal method for giving a shell accuracy. The centrifugal force disperses the jet, so the warhead design needs to be modified for use with rifled guns, or fired from smoothbore weapons.Pretty cool, huh? Let's list some main points:

* As a HEAT warhead relies on a shaped charge to move superheated metal at supersonic speeds into the armor, the velocity of the round delivering it to the armor is inconsequential, unless you are a rank crook-pated fustilarian.
* Rotational movement disrupts the jet of superheated metal which is why you will not see HEAT rounds being dependant on high velocity delivery which would require a large amount of rotational force to maintain ballistic energy.
* Velocity of the projectile DOESN'T MATTER as long as it can hit as hard as a softball to activate the explosive charge.
How now, my sweet creature of bombast? Now we have established my main point, from here we will attack boosters and the launch sequence and finish up at the penetration of rolled homogenous steel.

Boosters. Let's use an image of the launch sequence to get this nice and firm in everyone's mind:



Launch is by a gunpowder booster charge (from now on I will use the accurate term 'launch charge') at 115 m/s, which creates a typical tell-tale cloud of light grey/blue smoke. The rocket motor ignites after 10 meters and sustains flight out to 500 meters at a maximum velocity of 295 m/s.

Stop, and read that again. The launch charge is a simple low explosive that kicks the rocket out to ten meters away where the engine can ignite without roasting everyone. It only serves the purpose of getting the rocket out to a few meters away at a relatively low velocity of 115m/s, or 350fps for our non-metric friends. My pellet gun shoots harder than that.



Now, the launch charge (the stick piece) is stored seperately, if I hunt up a picture of an RPG operator's backpack with the grenades sticking out of one part and the launches stored in loops below. This is for compactness, if the launch charges were built into the grenade it would make them even more unwieldy and also difficult to replace if damaged or defective. The launch charge is necessary to kick the warhead out for the main engine to ignite and you can't double up launch charges. Also, the launch charge has zero, no, nada, zip, effect on the velocity of the warhead. It does not "boost" beyond a few meters.

As for penetration, the PG-7VR (told you I'd come back to this) is a Tandem Charge HEAT warhead. A tandem charge has two stages of detonation, mostly to defeat reactive armor. It will defeat reactive armor and continue penetrating Rolled Homogenous Steel armor for nearly twenty-four inches. When I said an RPG round can penetrate two feet of armor, I knew what I was talking about. The PG-7VL normal HEAT comes in second with nearly twenty inches of penetration of normal rolled homogenous armor without a reactive layer. Simply perform a little research and you will see that the PG-7VR is widely known to penetrate 600-650mm RHA armor.

Thank you for reading and please remember this post every time that frothy motley-minded hedge-pig wants you to take his words seriously.

References:
RPG-7 at guns.ru
RPG-7 at Global Security
Wikipedia entry on RPG-7
How Stuff Works on the RPG-7
HEAT warheads
PG-7VR
Tandem Charge
Defense Update on the RPG-7

Thousands of such references are easily available to anyone who wishes to look. Thank you and goodnight.

The Rabbi:
Some people have waay too much time on their hands.

The Rabbi:
Actually I was thinking of the people who bothered to read all that crap.

Polishrifleman:
Note to self "don't argue PRG's with Blackburn" he's even got diagrams and stuff.

Harold Tuttle:
they make a good catfishing tool:
http://sayanythingblog.com/2006/04/30/rpg_fishing/

Navigation

[0] Message Index

[#] Next page