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Aluminum Cases   General Military Discussion

Started 5-Aug by JesseH1234; 2043 views.
stancrist

From: stancrist

7-Aug

The fact that "part of the aluminium case is actually burning" is quite different than what my comment addressed.

Renatohm said that burn thru "may generate a thermite reaction...the aluminum will burn through bolt, barrel and whatever else is in the way."

You don't seriously think that burn thru would make the aluminum cartridge case act like a miniature thermite grenade, do you?

EmericD

From: EmericD

7-Aug

stancrist said:

You don't seriously think that burn thru would make the aluminum cartridge case act like a miniature thermite grenade, do you?

No, because in a thermite grenade it's the liquid iron produced during the reaction that is making most of the destructive work, but as shown in the paper you linked, the gun erosion produced by the "burn thru" mechanism is much more severe than damage produced by a gas leakage with conventional brass case, because aluminium burning is exothermic.

stancrist

From: stancrist

7-Aug

EmericD said:

as shown in the paper you linked, the gun erosion produced by the "burn thru" mechanism is much more severe than damage produced by a gas leakage with conventional brass case, because aluminium burning is exothermic.

Nevertheless, solid aluminum is not thermite, and does not burn like thermite.

Thermite is powdered aluminum mixed with a powdered oxidizer.  When thermite is ignited, it will continue to burn until completely consumed.

The cartridge case is solid aluminum, and the only available oxidizer is in the propellant.  Once the propellant is consumed -- which occurs in a fraction of a second -- the aluminum case stops burning.

It is simply not possible for an aluminum cartridge case to "burn through bolt, barrel and whatever else is in the way."  There can be no "thermite reaction" when there is no thermite.

EmericD

From: EmericD

7-Aug

stancrist said:

Once the propellant is consumed -- which occurs in a fraction of a second -- the aluminum case stops burning.

Not totally according to the papers you linked, as Al reacts mainly with H2O, which is a byproduct of the primary reaction (so even when the reaction stops, H2O remains), to produce aluminium oxide and hydrogen, that could later mix with air to burn again (hence the large and bright plume on the various pictures as shown in the report).

But I agree that the aluminium case will not "burn through bolt & barrel", it will just severely erode those parts and render the weapon inapt for service, and try to harm the soldier in the process.

Just for the record, during the peak of the "FAMAS crisis" in 2008-2009, we had 1 out-of-battery explosion for ~500,000 cartridges fired, and it was ten times more than what is OK for a front line service weapon, and the report is talking about 1 "burn-thru" out of 25,000 rounds with aluminium cases, so even with a reliability increase of a factor 20 the Al case would still be a major problem...

QuintusO

From: QuintusO

7-Aug

The issue is actually that ACs don't fire anywhere close to as many rounds as small arms, and when they have problems no one's nearby. If 1 in a million autocannon rounds burns through, you might lose a barrel every 100,000 sorties. If the same rate of SAA fails, that's 1,000 injuries and close calls every year.

stancrist

From: stancrist

7-Aug

EmericD said:

stancrist said: Once the propellant is consumed -- which occurs in a fraction of a second -- the aluminum case stops burning.

Not totally according to the papers you linked, as Al reacts mainly with H2O, which is a byproduct of the primary reaction (so even when the reaction stops, H2O remains), to produce aluminium oxide and hydrogen, that could later mix with air to burn again...

Picky, picky.  The aluminum stops burning a fraction of a second after the propellant is consumed.  It doesn't keep burning until the entire cartridge case is consumed, unlike thermite, which burns until there is none left.

EmericD said:

Just for the record, during the peak of the "FAMAS crisis" in 2008-2009, we had 1 out-of-battery explosion for ~500,000 cartridges fired, and it was ten times more than what is OK for a front line service weapon, and the report is talking about 1 "burn-thru" out of 25,000 rounds with aluminium cases, so even with a reliability increase of a factor 20 the Al case would still be a major problem...

Certainly.  Which is no doubt a big reason why aluminum cases have not been adopted for rifle ammo.

  • Edited 07 August 2020 16:36  by  stancrist
EmericD

From: EmericD

7-Aug

Picky, picky.  The aluminum stops burning a fraction of a second after the propellant is consumed.  It doesn't keep burning until the entire cartridge case is consumed, unlike thermite, which burns until there is none left.

Ah, OK, but it's just because the propellant does not produce enough H2O to burn a significant part of the case (the oxygen balance of most powders is made to avoid complete oxidation of the final products, hence the secondary flame found on most weapons).

Yes, in the case of a thermite, the balance of oxidizer and fuel is properly done to achieve a complete reaction, and as I said previously, in the case of a thermite it's the liquid slag (mostly composed of iron) that is doing most of the demolition work, we don't have this liquid slag in the case of a "burn thru".

nincomp

From: nincomp

7-Aug

EmericD said...

Just for the record, during the peak of the "FAMAS crisis" in 2008-2009, we had 1 out-of-battery explosion for ~500,000 cartridges fired, and it was ten times more than what is OK for a front line service weapon ...

At the risk of derailing this thread, I am unfamiliar with the "FAMAS crisis."  Would you please go into a little detail of the problems and what was done to fix it?

Thank you.

JesseH1234

From: JesseH1234

7-Aug

Thanks!  I asked for it, and I got it. 

Skipping through the larger one, the first thing that comes to mind is maybe once in a while they got a powder charge with a bit of excess oxidizer in there.

EmericD

From: EmericD

8-Aug

nincomp said:

At the risk of derailing this thread, I am unfamiliar with the "FAMAS crisis."  Would you please go into a little detail of the problems and what was done to fix it? Thank you.

Well, to keep a long story short... at the end of the 90's, it was decided to stop making small-arms ammo in France for the FAMAS, and buy ammo on the international market. For several reasons, people first bought SS-109 ammo which of course didn't delivered the expected results out of the 1-in-12" barrel twist of the FAMAS F1, then after buying a large amount of M193 from an oversea manufacturer, we started to see out-of-battery explosion in the FAMAS F1. The peak of this crisis was around 2008-2009, with more than 30 destroyed rifles during this period.

The shooters were not harmed, but soldiers were rapidly losing confidence in their rifles, so 3 actions were launched:

- trying to find why those FAMAS were exploding,

- trying to find ammo on the international market that were compatible with the FAMAS action,

- replacing the FAMAS (that was the beginning of the AIF program).

While we didn't find exactly the reason of the FAMAS explosions, the most probable explanation was that those accidents were related to a "bad" behavior of the soldiers. During live-fire training, you could encounter failure to feed with badly deformed rounds. Those rounds should not be fired but brought back for re-integration and destruction, which needs paperwork. Soldiers preferred to partially chamber the rounds, and strike the top mounted charging handle with an empty mag until the bolt was sufficiently closed to allow firing (you can't do that with most rifles). This course of action was OK with the steel case rounds, but not with brass case rounds.

Anyway, finding M193-family ammo compatible with the FAMAS action was not much of a problem (but involved firing several millions of rounds), so the "crisis" ended with the issuing of ammo from Lake City, BAé, MEN and CBC, and that give us enough time to launch the AIF program which ended in 2016 with the selection of the HK416 F.

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