Looking for an answer

[JimNM]

Hey y'all, I have long wondered why a round nose pellet leaves a splash mark with a dimple on a metal surface. Painted or not, I have seen this effect for as long as I have been shooting AIRguns.

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These were shot against an AR400 plate at 75 yards. The .22 Seneca pellets are not the only ones that leave this mark, my AA domes do as well. I have my theory, but want to hear from the collective mind before I spout off and show my ignorance.

Cheers

 

[L.Leon]

Is it because only that tiny bit of the lead dome is vaporized at impact? That's my guess.

 

[18.13]

When I shoot steel targets at night you can see sparks 

 

[Healthservices]

The lead pushes the paint away as it collapses against the steel. It pushes out as well as in. What you see in the middle is what it pushed in wards? 

Anybody have a ultra high speed camera laying around?

 

[Healthservices]

Looking at the few pellets that have hit steel I find they are not totally flat but actually a little concave. That concave spot corresponds to the little paint spot on the steel. 



Anywho thats my theory... 

 

[JimNM]

+1 to Healthservices. IMHO, the pellet collapses on impact. Near the center of mass, the vector of movement is in line perpendicular to impact. At that point the force is straight on to the steel so there is no side slip of the lead. The farther away from the center of mass, the more lateral the lead will deform. The ridge around the impact shows how the pellet pushed the paint away from the middle in all directions almost equally. It makes sense inside my head, anyway. It does make measuring center to center pretty easy

 

[sticman77]

I agreement with the others…. I think. Looks like that’s part of the pellet stuck on there where the force was more head on.

can you scrape those dimples off?

 

[JimNM]

Dimples in this case are paint . 

 

[sticman77]

Well scratch that! Re read healthservices explanation makes more sense now that I am not thinking the center is paint.


on a macro level shouldn’t craters have a similar center dimple? Or would the difference in hardness of projectile vs impact surface make it too different. A google image search yielded some but few examples of craters with center dimples 

 

[JimNM]

The center dot IS paint 

The high speed camera would be cool to play with. Anybody have myth busters abilities?

 

[Vetmx]

Friction equals heat. When the very tip of the dome strikes the paint on the plate, the amount of heat created for that micro second bakes the paint into the pores of the metal.