SpudFiles

Well I was shooting my <A HREF="http://www.spudfiles.com/forums/viewtop ... 28">SGP</a> gun today at a piece of 20mm chipboard, I decided to move from paintballs to fishing sinkers.

I fired a shot of at the board at 110psi, it went straight through and with closer inspection the sinker had hit a piece of rope holding the board to a backing. Well take a look at the pictures and see for yourself.

WOW!

Have you considered that your cannon may be too powerful?

Me neither. A guy can never have too much power.

are you sure its rope burn?

not just the imprint of the rope on the fishing sinker because at that psi or lower the fishing sinker pancakes a bit upon impact, and that could have been the case?

(if that makes sense)

^^Maybe...but it sounds cooler calling it rope burn.

Well yeah, the energy involved would of created enough heat to burn through the lead which has a low melting temp.

I just said rope burn because its more or less what it is, rope burning(well melting) through lead, I doubt the rope is hard enough to imprint the sinker from pancaking.

Also since the imprint goes around the sinker in a curve shows that the sinker was caught by the rope and was directed slighty by it, it was probably spinning when it hit the rope and thats why the imprint follows it around. If it pancaked against the wood it would only be a few mm long.

I fired an airgun pellet at a file once, got a lovely diamond pattern

Even firing lead pellets at fabric will leave a distinct impression on the face of the projectile.

Funny, i fired a lead sinker at a folded piece of s/s wire mesh today that was sitting on concrete. The front of the sinker looks as though it had been put through a mincer

Yeah I am just surprised I hit the piece of rope, I was 15m back, I'd be lying if I said I was aiming for it

Here's something I did with the hybrid that I forgot to post before, but since it relates to this topic I'll still share it.

One of the test firings was a lead ball shot at a brick. On impact the brick was broken in half and the chunks went flying backwards.
After a while I found the ball, which now looked like this:

I don't think the lead was melted by the rope, rather the rope just pushed an indentation into the lead. (Lead is soft enough to scratch gouges out of with your finger nail)
The fact that there is a rope patter in th lead is more evidence of this scenario, not to mention I think the rope would be in a pretty sad state if it had come in contact with lead at its melting point.
Either way, pretty cool to effect to see.

MrCrowley wrote:Well yeah, the energy involved would of created enough heat to burn through the lead which has a low melting temp.

Well, not quite.
To heat a mere 3.5g of lead to it's melting point, assuming it started at 25*C (Room Temp), takes ~135J of energy.

GGDT puts your cannon at around 75J for this shot, just over half the energy required to melt 1/8th of a 1oz fishing sinker. Of course, even if we say the gun produced a muzzle velocity of 100m/s, there would only be ~140J contained within the shot. All of that energy would have to somehow be focused on the 3.5g of the sinker mentioned earlier to melt the lead to liquid. This sort of efficiency of energy transfer under conditions such as these is no where near practical.

True the lead's temperature may have been slightly elevated, making it more susceptible to forming around the rope, but this is an indentation, not a "burn mark".

So when the sinker hit the rope, it was spinning and it managed to do half a spin on the rope before it broke through the wood?

If it was a head on collision with the rope the indention would only be so long and not continue around the sinker, but that only applies if it wasn't spinning, which I highly doubt.

The rope looks to have continued to wrap around the sinker as it was breaking through the wood. This will also make it easier for the lead to press against the rope hard enough for an indentation to show up.

You can also see that the rope has cut through the wood, so that backs up your theory of it continuing to wrap around the sinker after breaking through the wood.

I hadn't even payed attention to where the rope cut through the board, I see what you mean.

I still have to say, indenting the the intricate pattern of a rope on a lead ball is pretty damn cool. (I would love to see some clear pictures if you can get another camera.)