So a friend of mine said to me a short while ago that when a HEAT weapon like the RPG-7 manages to penetrate armour, it creates a pressure wave so immense that the crew are "forced out the hole" leaving "only bloody pulps and clothes".
Now, he obviously doesn't literally mean forced out the hole, that's just giving a mental image of the impact. But for an 85mm warhead, with a penetration of just 260mm, it sounds far more damaging than it ought to be capable of.

I could easily imagine this effect with a tank-round sized HEAT warhead, or an APFSDS round, but an RPG warhead just seems to small to have anything like the effect. Is he right? He has served by the way, but not as a tanker.
It just makes using a tandem DU cone specifically for after-armour effects completely redundant if the effect is already that violent from the penetration.

And why doesn't adding additional tandem warheads in HEAT rounds give cumulative RHa penetration? Sumer said it, but can't remember if he explained it or not. He just stated that a precursor round would penetrate ERA/add-on armour, the main charge would blast through the armour, and the third charge would only be used for after-armour effect.

No. Tanks have been penetrated by HEAT rounds and the crew have survived. Eg here. The explosion occurs outside the armour, after-all. LRP should be the same.

That's not why either things are used. At least, in the case of DU, not the main reason.

Ideally, it does. But the reason to have a precursor is to prematurely detonate the ERA with a charge that wouldn't otherwise penetrate the ERA, which saves weight in the warhead, so the basic cumulative (pen1 + pen2 + ...) penetration would in fact be lower than the actual.

It was back when ASE was throwing around the idea of 140mm triple-tandem DU HEAT warheads for his tanks in NS's MBT thread. Sumer came along and said that realistically, the three warheads don't accumulate (at least, not directly) and because of this, the best reason for a DU final charge (specifically referencing the third charge) was for after-armour effects.
Presumably, because pyrophocity[sp].

Training round LRPs in British service have anecdotally been known to cause tanks to blow apart because of overpressure upon penetration.
Taken from a TV show in which they tried to use a training round LRP, fired from a Chally 2, to crack an 'unbreakable' safe. The round merely glanced off of the safe, having hit in on a corner, but it tore a bloody great gouge in its armour.

They probably wouldn't in practice - there have been similar proposals, but they would need to line up exactly. And then the question is why bother, when you could just make a single, larger warhead that would be more efficient?

In practice it doesn't matter, because that isn't why tandem charges are used. The first charge is just there to detonate the ERA plate. It doesn't need to penetrate it, just set it off so that the main charge can finish the job.

If you're proposing to put a separate charge behind the main charge to pass through the hole into the tank, you wouldn't use a HEAT warhead, but a fragmentation warhead (like a hand grenade). However the 'hole' cut by HEAT jets is qutie small, and I've never heard of that being done IRL.

Tanks don't spontaneously blow apart - that would require an ammo cook-off. Also not sure what a "training round LRP" is.

How does that imply a large internal pressure? If the round never even entered the safe that sounds about the opposite of a relevant example.

Training round LRP is just an APFSDS round intended for training tank crews. Ergo, cheapo steel penetrator.

The 'blows tanks apart' was how they described the power of the LRPs, before unsuccessfully engaging the safe.

The theory was not explained (and I was many years younger at the time), but was probably related to:
>LRP enters tank
>compresses internal air because of velocity
>air blasted out when LRP clears its entry hole
>tank 'explodes' from pressure
Which is probably not correct on any level, but seems to be how they were describing it.

It sounds more like an inaccurate throw-away description by someone who didn't know what he was talking about, from an unreliable source. If you read the article I linked, this is roughly the process by which you get from "British tanks are heavily armoured over the front portion against threats that existed at the time it was designed" to "British tanks are invincible".

The actual examples of tanks not blowing up from overpressure when penetrated in combat are more compelling.

The drastic effects caused by "over pressures" created during an armour penetration event are an old story that keeps popping on more or less respectable websites and has been consistantly shot down. The lcoationa dn time of the event described does shift a bit, i've seen it claimed to be from veitnam, various arab isreali conflcits, india/pakistan conflcits and the Iran-Iraq war.

There is a lot going on during a penetration event and soemtimes odd occurances happen that some put down to over pressure effects but to be honest msot of them happen for far more mundane reasons like the shudden shock causing a commander to lose his balance and feel like he has been thrown from the tank.

The LRP effects are often the msot lurid including such claims as with a complete through and through the penetrator actually sucks the crew out through the roudns exit hole.

In actual fact msot HEAT penetration involve a thin rapidly cooling jet of metal that flies through the hull space boucnes off the interior and few times and stops, generally only injuring crewmemeber that are in its direct path. Higher order shaped charges with more armour over match do produce somewhat nastier effects and when the liner material is soemthign like aluminium or DU you get lots of secodnary burny effects and possibly a liner that fragments psot penentration.

A third stage on a tripple stage HEAT warhead is mainly there for behind armour effect either by creating a secondary divergent penetration path or to inject a liner with pyrphoric of fragmentatry characteristics. A follow through charge/grenade would be preferable but you need a main stage that is designed to create fairly wide holes to make them viable. As to cumulative penetration its as Prae said getting a pair toc ahrges to line up precisely and detoante in such a way as to create a single jet if so dificult that ultiamtely a single big main charge works better.

According to "AMMUNITION SERIES SECTION 2, DESIGN FOR TERMINAL EFFECTS"

Live fire tests with 5 inch aluminum shaped charges, tanks and live animals in the 60's measured a peak pressure of 50 PSI inside the tanks. The animals were unharmed by the pressure, but it did damage some equipment inside the tank.

So the pressure isn't going to be killing the crew.

Do you have any sources for this? Not saying you're wrong, but I haven't heard of this in the past, and looking now, the only reference to triple charges even existing seems to be a single sentence about a Russian round copy-pasted onto a dozen websites. If there's something with more detail I'd be interested to read it.

Then there is BROACH, which is uses a shaped charge to blow a hole for a conventional explosive to follow, although since it's not designed for use against tanks and is a lot larger, may be optimised differently.

On the tirpple stage system the only thing i've ever been able to find relaibly was the breif mention of 3BK-31 on Vasiliy Fofanov's site http://fofanov.armor.kiev.ua/ which si what you'll see CPed everywhere else. I'm sure I've read other stuff and posisbly buried it in the mess that that is my bookmarks folder. To behoenst i've likely extrapolated of shaky ground and misremebered details but it does sound vaguely logical.

The likes of BROACH, the FTG warheads for B-300/SMAW/Shipon and the M150 PAM: http://www.globalsecurity.org/military/sys...itions/m150.htm all seem to be optimised for concrete penetration. In the case of PAM the charges are set up to create fairly wide penetration channels.

Well that is interesting. Lends some weight to the idea that this is a follow-through charge. Still, it seems odd. First, if it's to get DU involved, why not simply make the main charge liner out of DU? And second, if it's just to introduce a second HEAT slug, seemingly moving in a very similar direction, is that really worth the weight? Since the charge is smaller, it's going to have to pass through the hole made by the central charge anyway.

Perhaps this is actually an attempt to increase penetration by successive stacking charges, but today I think this is done more efficiently with improved liners &c. At least if it were a good idea, I would expect it to have spread by now.

There was also a triple charge design tested by Nammo that used a main charge with two precursors.

I've seen a picture and had the patent once.

I don't think that 3BK-31 was actually intended for DU and actually was an attempt atincreased penetration. IIRC the middle charge is actually the last one to "fire".

From i cna gather from what Vasiliy has provided the forward charge deals with ERA and then the rear charge fires to open a hole through the start of an armour array and its jet is setup to be slightly out of alingment so that it isn't in the way of the middle/third stage jet when it fires.

Ultimately i don't think it really gave them the improvements they had hoped for and as i said i'm probabaly guilty of extrapolating the possibility of using something interesting as the liner on a third stage to increase behind armour effects