What causes this?

[amlevin]

The other day I was at the range shooting my AR. The load was 27.8 grains of AA2230 under a winchester bulk 55gr FMJ-BT. Sort of an M-193 pretender load.

While shooting, the rangemaster came in and stopped me. He asked what I was shooting as I was creating a shower of sparks from the bullet trap. He thought I had SS-109's and the steel was causing the sparking. The winchester projectiles, as far as I know, are lead that is swaged into a copper jacket.

Every shot was throwing a large spark back onto the floor, much like someone striking a zippo lighter and having the flint shower sparks.

The only thing I could think of was that there was a lot of buildup of unburned powder residue and carbon on the bullet traps. These traps are the type with verticle apetures, steel plates slanted to the apeture, knife edge blades separating each "section" and the bullets are directed into a vertical "scroll" that slows and traps the bullet. There is a lot of air that is drawn through the trap and if there is powder residue and carbon that has collected on the surface, that 3150 fps bullet may be igniting it and splashing it all over. Just my thoughts. Any other Ideas or answers out there?

Just curious.

 

[Galil5.56]

Have you chronographed this load? Your charge is pretty stout (almost 2 grains over my circa 1992 manual/over current max by almost 3 grains) for commercial brass, and If used in military brass I wonder if there are any signs of hi-pressure? Not trying to stir up anything, just curious if/how you worked up this load and the velocity you got.

 

[Grumulkin]

Over pressure or high velocity won't cause sparks in a bullet trap. I suspect the bullets are indeed steel jacketed.

 

[tunnug]

easy enough to tell if they are steel jacketed, put a magnet to them and see if they stck.

 

[amlevin]

There are no signs of overpressure, either in the case or primers.

As for the bullets being magnetic, I checked them with a strong Alnico magnet and the rangemaster also checked. Non-Magnetic cases.

 

[JRadice45]

It could be due to the high velocity. A friend of mine owns an AMT Automag in 30.carbine, Not only does it have a wicked muzzle flash, but upon hitting the backstop, the spark display looks like a starburst firework.
This was using carbine ammo he loaded.

 

[ants]

Maybe the core is "Hollywood" lead. In Hollywood, all lead bullets make sparks.
Don't tell me they don't, because I've seen all the movies. It's true!

 

[1911Gunslinger]

High velocity copper jacketed bullets will cause sparks apon hitting steel. The mass of the bullet traveling at high speed causes a displacement of a small amount of steel material on the surface of the plate and because of the high amount of friction present the metal glows as it is displaced, hence the sparks.

 

[Jeff F]

+ 1 to what 1911Gunslinger said.
High velocity copper will cut through steel like a hot knife through butter. I have worked in blasting and demolition and we use a copper lined V shaped charge to cut steel. Its the high velocity copper that does the cutting

 

[amlevin]

Thanks 1911 Gunslinger and Jeff F. Now that you brought it up it makes perfect sense.

I guess that I should "turn down the wick" a little on my loads if I want the sparking to go away. Although, there is a somewhat satisfying feeling knowing that your rounds are going fast enough to "hurt" solid steel.