The little dot left on bell target surrounds

[trajectory]

I'm not sure if this post should be in the Target Shooting or General forum but on balance I thought the pool of knowledge & experience of the contributors to the Collectable section might provide an answer to the following.

When a round nosed pellet is fired at the painted target plate of a bell target it leaves a central dot or spot but what's the explanation for this, why dosent the leading part of the pellets nose displace the paint at the centre of impact?

Is it because the paint is indeed initially displaced but the rest of the face of the pellet impacts the target before the paint has fully flowed away from the impact area & as the pellet is hollow based the greater mass of lead around the circumference collapses on the head but the lower central mass dosent hit the centre of impact so hard & therefore leaves the central dot?

Maybe Ive not explained this very well but is it something along those lines or am I way off? Just wonder what the explanation really is.

[Unframed Dave]

A vacuum is formed by the deforming pellet, this sucks a drop of paint into the centre.

Dave

[zeroscore]

A vacuum is formed by the deforming pellet, this sucks a drop of paint into the centre.

Dave

some good knowledge here

[trajectory]

Thats intriguing, do you know how it forms a vacuum or where there might be a bit more information on how it happens please? I'm trying to visualise it but can't get round that the leading part of the nose of the pellet hits first & as it deforms the rest of the pellet flattens ( sequentially... if that's the right word) but starting centrally & moving outwards thus dispelling any air... Just wondering about the mechanics of the process. Cheers

[Unframed Dave]

Thats intriguing, do you know how it forms a vacuum or where there might be a bit more information on how it happens please? I'm trying to visualise it but can't get round that the leading part of the nose of the pellet hits first & as it deforms the rest of the pellet flattens ( sequentially... if that's the right word) but starting centrally & moving outwards thus dispelling any air... Just wondering about the mechanics of the process. Cheers

I can visualise it in slow motion in my head, but I'd need a pen and paper to demonstrate it to another person.

Dave

[trajectory]

I can visualise it in slow motion in my head, but I'd need a pen and paper to demonstrate it to another person.

Dave

Hi, is it that the impact of the pellet dispels all the air on impact but on 'bouncing' off air rushes back into the space ahead of the pellet where a moment before there was nothing.......something along those lines maybe?

[Unframed Dave]

Hi, is it that the impact of the pellet dispels all the air on impact but on 'bouncing' off air rushes back into the space ahead of the pellet where a moment before there was nothing.......something along those lines maybe?

It's the expansion of the head outwards. As the metal expands outwards, I imagine it like a the front section of an inner tube forming initially which then flattens out as the back of the pellet catches up with the rest. Like I say, it's not an easy thing to put into words.

Dave

[WebleyWombler]

It's the expansion of the head outwards. As the metal expands outwards, I imagine it like a the front section of an inner tube forming initially which then flattens out as the back of the pellet catches up with the rest. Like I say, it's not an easy thing to put into words.

Dave

From the way you have explained it, wouldn't a better analogy be the rubber sucker the end of the arrow on a toy bow or dart. that works on the same principle but the skirt is flexible to maintain the vacuum. a pellet is more rigid and doesn't have the same sealing capacity so the vacuum effect fails and the pellet doesn't stick?

[trajectory]

It's the expansion of the head outwards. As the metal expands outwards, I imagine it like a the front section of an inner tube forming initially which then flattens out as the back of the pellet catches up with the rest. Like I say, it's not an easy thing to put into words.

Dave

Thanks for that, I think I'm beginning to see what you mean. As you say some things are easier to explain than others but definitely appreciate your help. Still find it intriguing, & it's a very handy physical phenomenon for bell target shooting, cheers

[Turnup]

I really cannot see how a vacuum can cause the effect but I have an alternative theory

I have seen slo mo closeups of a round nose pellet striking a hard surface. At the instant of impact only a small part of the nose is in contact with the plate and this generates a very high pressure in the lead at that point - so high that the lead liquefies (not melts) and a tiny jet of liquid lead is ejected out of the back of the pellet. This leaves a small cavity and as the rest of the pellet arrives there will be flow inwards to the centre of initial impact.

I think it would be instructive if someone were to test the effect of a hollow point pellet and a flat point pellet and a pointy pellet.

[Unframed Dave]

I really cannot see how a vacuum can cause the effect but I have an alternative theory

I have seen slo mo closeups of a round nose pellet striking a hard surface. At the instant of impact only a small part of the nose is in contact with the plate and this generates a very high pressure in the lead at that point - so high that the lead liquefies (not melts) and a tiny jet of liquid lead is ejected out of the back of the pellet. This leaves a small cavity and as the rest of the pellet arrives there will be flow inwards to the centre of initial impact.

I think it would be instructive if someone were to test the effect of a hollow point pellet and a flat point pellet and a pointy pellet.

I have tried with flats and it doesn't happen. Not the others though. Also works much better with soft alloy pellets than hard.

When I set up the bell target club, I trialled a lot of pellets, mainly for "splash back distance".

Dave

[ptdunk]

How about this:
As per Dave’s vacuum idea.
The centre of the domed head comes into contact with the target plate first, and starts to bounce back as the sides of pellet head come into contact with the plate, sealing it off and creating a vacuum?

Effectively the tip of the pellet begins to bounce back a fraction of a second before the rest of the pellet.

Just an idea.

I always wondered why dome heads leave a pip, and not flat heads...we have to use them for bell target for exactly this reason as it makes it easier to score.

Cheers,
Matt

[Solvo]

It's a fun bit of terminal ballistics.

As the lead pellet hits the immobile surface the energy the pellet carries has to go somewhere.
It 'washes' outwards, the pellet expands in all directions away from the centre, the outward movement carries off the paint from the target.
The only area of impact where there is no movement is the tiny point at the centre. How large the point is depends on the velocity of the pellet and the softness of the lead.
The pip in the middle is the central point where there isn't enough force to push it outwards, the cone left is effectively the same as the 'Angle of Repose' you can measure in any material as it piles up, but in this case it's horizontal and solid as it's being formed by the ballistic energy of the mass rather than gravity pulling bits of material downwards.

As mentioned earlier the tail end of the pellet catching up can also 'stick' to the pip making some interesting shapes as there's no longer enough energy left for the last bit of material to wash outwards. More visible in pellets with solid mid sections such as Accupel and less so in hollow points with deep skirts (Like Super-H) as there's less central material to form the pip.

The same effect can be created by launching a malleable material at a solid plane, think ball of plasticine into concrete for example.

Edit: Effect shown in image B on this page: https://nelson.mit.edu/news/situ-stu...impact-bonding along side rebound and deflection. Image B shows around the half way the outward splash effect. With lead pellets this out wash can be found in the lead debris as wide semi circular splayed rings of pellet fragments.

[T 20]

I try to get my pellets through the little hole in the middle of the target so that I don't mess up the paint.

[trajectory]

Very interesting replies, from everyone.
In the past I have seen the 'pipping' with domed pellets & learnt that they were used in bell target shooting for this reason as other styles don't produce the same effect. I had also noticed that some domed pellets fired perpendicularly to a flat steel surface have a tendency to almost turn themselves inside out & moderate velocity pellets thus fired often display a central pip on the non impacting surface although the impact surface appears pretty uniformly flat. Not sure what the implications of that are but on reading Solvos excellent terminal ballistics explanation it made me wonder if / what the minimum / maximum velocity of a RN pellet might be if it were to produce a pip on a bell target. Bell target rifles have to be below 6 ft/lb, so does a very low sub 6ft/lb velocity produce the same effect? Conversely is there a maximum velocity beyond which the phenomena ceases to be (way above 6ft/lb?)
I think I need to have a plink at some paint....