Interim Incendiary Solution (Modeling Low Explosives)

[DJBscout]

Currently, US .50 cals do not have their incendiary rounds modeled in game.

 

This leads to underwhelming performance in comparison to HE-based MGs.

 

However, I may have a (temporary) solution.

 

The incendiary composition in most rounds was very similar to what we would call flash powder today. Now, flash powder is not the same thing as TNT/other high explosives, and is generally considered a "low explosive". However, it is still far from inert. Specifically, per this DTIC which I will be referencing extensively,

Quote

"Most small arms incendiary compositions are mixtures of metals (or metal alloys) and an oxidizing compound in some type of an explosive. These mixtures are usually initiated by impact or friction and burn rapidly. In some cases they burn with explosive violence. The output must be greater than the target initiation temperature, and the duration of the flash must be sufficient to cause initiation of the target."

Furthermore, a "photoflash charge" is described as an

Quote

"unconsolidated mixture of pyrotechnic ingredients that, when ignited, produces high temperature, high gas pressures, and a rapidly expanding flash-cloud"

High temperature, overpressure, and an expanding gas cloud. That's remarkably similar to an HE cloud.

 

So, what exactly did the US use, and what was it made of? The US used a number of different incendiary rounds. 

 

The first is the M1 Incendiary round, which carries 34 grains (2.2g) of IM-11. The second would be the M8 API, which carries 15gr (.97g) IM-11. (In the patent, it is claimed that M8 packs IM-28, not IM-11, but as the patent is from 2016, it would not be surprising if the M8 round was changed to IM-28.)

 

The third is the late-war M23 "super incendiary", which packs in 90gr (5.83g) of IM-28 (being pretty much just a jacket packed with IM-28).

 

IM-11 (source: patent by US army) is a 50/50 mixture of Barium Nitrate and Magnesium Aluminum Alloy. 

 

IM-28 (source is again the patent) is 10% Potassium Perchlorate, 40% Barium Nitrate, and 50% Magnalium (in this case specified to be a 50:50 Mg:Al mix). 

Spoiler

Magnalium's composition varies. The patent describes the mix used as "A chemical alloy of aluminum and magnesium said magnalium comprising 10:90 to a 20:80 ratio and more preferably 50:50 ratio of aluminum to magnesium"

 

This leaves a wide range of possibilites, though the concepts of flash powder generally remain the same.

So, how powerful are these compositions?

 

Short version: While details can be somewhat hazy, the TNT RE (relative equivalence) of flash powder comes out to ~.42. 

 

Long version: This paper (same DTIC from earlier) goes quite in-depth on the high reactivity of such low explosives, including TNT equivalences. Generally, photoflash mixtures were found to have have an RE of .36±.12. (However, it should be noted that the highest was actually .56) 

 

Frustratingly, while a mixture almost identical to IM-11 in terms of material ratios can be found in the in-depth paper linked above, it was not tested for TNT equivalence. 

 

That being said, all the mixtures caused mushrooming in detonation tests (correlated with higher TNT equivalency values). The end result being:

Quote

At a minimum, a low order detonation can occur with specific illuminant mixtures. This is also borne out by reported TNT equivalency data. Colored and white light, and photoflash mixtures have TNT equivalency values ranging from a high of 56% to a low of 30%. These values are indicative of a reaction that is more brisant than would be expected from a deflagration.

 

Sound-producing formulas were also tested, and were in many ways similar to the photoflash mixtures.

Spoiler

The burn time data indicate that these mixtures burn rapidly, hence definition of the production of sound pyrotechnically was expected. The burn times reported for these mixtures are comparable to the photoflash mixtures reported previously. The average burn time was less than 400 milliseconds. Only two of the six materials under went TNT equivalency testing and they both were quite reactive. The M74A1 mixture has a TNT equivalency value of approximately 45%, and the M80 firecracker mixture had an equivalency of approximately 80%. These values are exceptionally high for pyrotechnic formulations.

 

Furthermore, the M112 photoflash also created a pressure wave and fragmentation under testing, similar to the M80. 

 

Spoiler

Anecdotal and imprecise, but you can see clear fireballs/flashes in the following videos:

https://www.youtube.com/watch?v=EwnVF1UoNEE

https://www.youtube.com/watch?v=11BAEBAC3Zg&feature=emb_logo

https://www.youtube.com/watch?v=3pEylQ2G5-U

https://www.youtube.com/watch?v=Ct_ZcEU0jds

Keep in mind that these videos are exclusively of API rounds impacting thick steel. The fireball is only from ~.97g of IM-11 or IM-28 (depending on the age of the M8 API), and the deformation from the explosion/deflagration is heavily limited by the thickness of the target.

 

Now, none of this is perfect.

 

EFFECTS:

• MG 131 HEI contained 1.4g of PETN (also some thermite)
  • (1.4*1.66=~2.3g TNT),
• M1 Incendiary contained 2.2g IM-11
  • worst(ish) case: (2.2*.36=.792g TNT)
  • mid-case: (2.2*.42=.924g TNT)
  • best case: (2.2*.56=1.23g TNT)
• M8 API contained .97g of IM-11
  • worst(ish) case: (.97*.36=.349g TNT)
  • mid-case: (.97*.42=.407g TNT)
  • best case: (.97*.56=.543g TNT)
• M23 super incendiary contained 5.83g of IM-28
  • worst(ish) case: (5.83*.36=2.10g TNT)
  • mid-case: (5.83*.42=2.45g TNT)
  • best case: (5.83*.56=3.26g TNT)

 

Even modeling 1/2 of US rounds as low-power explosives (incendiary rounds) would result in a massive increase to lethality within the current game, and would be far preferable to the current state of pure ball ammunition, which has precious little impact in the current game.