Steel core + metal target = fire danger, but steel jacket?

[grimjaw]

We have metal gongs at our range up on a hill. The hill caught fire earlier this year, but I never heard if it was due to sparks from one of the gongs or not. Regardless, they have stepped up enforcement of the "no steel core ammunition" rule, which I endeavor to follow anyway.

So most of the imported 7.62x39 has a "bimetal" jacket which commonly fails the magnet test. I've stripped the bullet for Golden Tiger down and confirmed the core is lead, but they range officer is concerned that the bimetal jacket can pose spark/fire risk.

I honestly don't know. Anyone care to weigh in?

jm

 

[grimjaw]

Nobody knows this answer?

 

[brighamr]

From my own experience, the only bullets that will actually start a fire are tracers. I know the spark from richochet theory, but I've never seen any evidence supporting it.

I've shot about 2000 rounds of Wolf FMJ at a truck frame (steel) with nary a fire, but this is just my personal experience.

 

[Geno]

+1 for tracer. A FMJ with metal core is NOT going to start a fire. but, I have seen tracers start fires. The other round that will quickly start a fire is the incendiary round. I think there are people who fire these believing them to be tracer, but they are not. They a white phosphorous...big time hot.

This would be a good one to send back to Myth Busters. They did one similar with gas tanks. There is a video about this too...PM me to remind me to look for the title later if interested.

 

[jaholder1971]

Some of the Talon tracer ammo I've seen have had the paint on the tips worn off making it indistinguishable from FMJ.

It's entirely possibe that some of this tracer was shot unknowingly. This happened at a sporting rifle match I was at once. The pits had to be unsealed to let the target pullers put out the fire. The shooter was using Talon ball that had a few tracers mixed in from the factory.

 

[230RN]

Pure speculation. OK? Pure speculation:

I would not be surprised if any fire that was started was because the bullet struck a hard rock in the backstop, not from any localized "flash" when it struck the gong.

Notice all the sparks when you see a video of a car dragging hunks of metal? And asphalt is not all that hard.

Think of a grindstone whizzing against a hunk of steel. Localized temps can be very high.

In addition, if iron gets hot enough, it will start to burn all on its own.

And it doesn't have to reach the ignition temperature from outside sources of heat. Get it warm enough, and the increased oxidation rate will accelerate the heat rise until it does get hot enough to burn. It is, in a word, mildy pyrophoric. (Like depleted uranium, but less so.)

Fires have started from iron cuttings, shavings, and chips getting wet. The oxidation rate keeps increasing until the iron is hot enough to self-ignote. The iron + oxygen reaction is very exothermic.

Welders know that once you start a cut with the oxy-acetylene flame, you can shut off the acetylene, and go on cutting just from the oxygen from the torch making the iron burn, releasing enough heat to continue the cut without any additional fuel (acetylene) required. At that point, the iron becomes its own fuel.

Also, up on the Grasslands in CO, there are many chunks of flint just lying around on the ground. I found one once that was about 2 pounds. I would guess hitting one of those with a steel (jacketed or cored) bullet might well throw a couple of sparks.

OK. Pure speculation. OK?

I suggest that anything moving along at >2000 fs striking something standing still will create very high temps. With lead and cupro-nickel, it wouldn't matter. But with steel, the iron in the small particles scattering might well ignite lighting up any tinder in the area.

Pure speculation, based on mechanical experience, not actual shooting experience, OK?

OK.

 

[Double Naught Spy]

Well, this is 55 gr. 5.56 ball ammo hitting a steel target from 25 yards at approximately 2900 fps. Sorry it isn't 7.62x39, but it is the only good impact/spark example I have. I just happen to think it is a really cool picture and finally found a place to post it.

You can most definitely make big sparks. You don't need steel core ammo to make them. HOWEVER, the sparks are very short lived. The visible flash seen in the attached file lasted 1/17th of a second or less (visible in just one frame of a camera filming 34 frames per second). So the metal superheats very fast and then starts cooling pretty fast as well.

The spark really isn't the salient point here. Bullets that impact the target do superheat and will be a several hundred degrees even without the visible spark. The question is whether or not they can then land in brush and start it on fire. You need what, 400-500 degrees F to catch leaves on fire? Certainly, the possibility is there, but with 10s of thousands of shots on steel targets, I have never seen this happen (as noted above).

Where is this going? I am not sure that the banning of steel core ammo is going to make any difference relative to fire risk when shooting steel targets. It may, however, make the targets last longer.

 

[Yosemite**Sam]

Steel core will start a brush fire

I work at a range as a full time firearms instructor. Just last week I watched a guy start a fire up on the hill above our range. He was the only one shooting uphill at a gong when the brush caught fire about 15-20 feet below the gong. I looked at his ammo and saw that he was using mil-surplus black tip (AP) 30-06 ammo. He definitely wasn't shooting tracer rounds. After the fire dept. arrived and put it out he decided to shoot paper targets with the bullet trap as a backstop. I stopped him after a few rounds due to the sparks it created upon impact. Sure enough his AP rounds were divitting the bullet trap. :banghead: