Paintball

[drg]

Speaking of this seam discussion, have you charted/analyzed the X displacement in shot placement, and, perhaps, the composite XY displacement?

[Fubarius]

Ok, after much pondering I have a theory why the matched bore produced more backspin than the overbore.

Now this model only works with closed bolts. Probably one of the few times where this actually makes a difference.

So you have the ball at rest in the barrel. It's being held by static friction. Now a brief review for those who haven't taken a physics class in a while. There's multiple types of friction between two objects. There's the friction between two objects not moving in relation to each other, called static friction. There's the friction of two object sliding against each other, called dynamic friction, or kinetic friction. And last there's the friction of an object rolling along another, called rolling resistance. In general, the coefficient of static friction is greater than that of dynamic friction. So it's harder to start something sliding than it is to keep it sliding.

So with a normal bolt and a bore matched barrel the air pressure disperses around the outside of the ball until it has enough pressure to break the static friction, and the ball starts to travel down the barrel.

Now take an undershot bolt. The focused air jet on the bottom of the ball pushes up on the ball and may slightly distort the ball, just a tiny bit, maybe one thousandth. Normally not enough to make a difference, but just enough to reduce the static friction on the bottom of the ball to zero, while maintaining the static friction on the top of the ball. This of course causes the ball to rotate as it starts down the barrel. Now the air pressure will stabilize as the ball travels down the barrel, but the rotation is already in effect. And since it's in a fairly short insert once it's past the insert into a much larger bored area there's no barrel wall friction to reduce the spin.

An open bolt gun would work completely different, since there's no static friction on the ball at the start of the firing sequence. I haven't puzzled how that would work yet. I'll leave that for someone else.

[cockerpunk]

Originally Posted by Schmitti

CP .. the ball deforms whether you see it or not. You proved it by being able to shove a .68 ball in a .67 barrel. And getting a ball moving from a standstill to 280 fps (190 mph) with friction acting on the outside of the ball and a force acting on the back of it (semi rigid body) is going to give you some deformation... not as much as a tennis ball getting wacked... but some.

And beach balls deform when you poke them... let alone kick them

E

of course the ball deforms at some point, but not from the air hitting it. not a measurable amount anyway.

[cockerpunk]

vid part dox - YouTube - CooperT Bolt Testing Methods and Results Explained

soon ill upload what i think about the rouge matched paint results.

[SSniper13]

Nice job guys. That set-up is very, very nice. I wish I wasn't swamped at school and work this week. You've now given me something to look forward to digesting in more detail this weekend.

SSniper13

[cockerpunk]

here is what i think -

YouTube - What I Think about the CooperT testing

[Schmitti]

of course the ball deforms at some point, but not from the air hitting it. not a measurable amount anyway.

We can prove this statement false because barrel breaks occur. If the ball never deforms you would never get a break. I've had breaks in clean barrels. I've had breaks at the breach from a clean load (no pinch). How do those occur if there is no deformation?

I'm not trying to be a prick... just stating that it happens.

But the ball deforming is not important..... the ball moving at the point of contact of the air is what would cause spin. Using the glass barrel, put a dual colored ball in the barrel with the seam allinged perpendicular to the direction of travel (so if it spins the seam will look like a paddle wheel)... then hit it with the undershot bolt and see what happens.

Yes I know.. Tom Kay has the glass barrel. Lets get it from him and see.

E

[russc]

Schmitti, I bet a slow motion barrel break would look pretty damn cool!

[Schmitti]

My favorite (for looks) are the combination liquid shot barrel breaks, where some how you've gotten a little bit of liquid through the valve (usually in the winter) and it hits the ball like a slug and you get the snowball effect from the co2 and the paint flakes. fun stuff and oh so frustrating when you try to clean it out.

In high school we played a lot in the winter over christmas vacation... it seems like we spent half the time cleaning this kind of break any time we played.

E

[cockerpunk]

Originally Posted by Schmitti

We can prove this statement false because barrel breaks occur. If the ball never deforms you would never get a break. I've had breaks in clean barrels. I've had breaks at the breach from a clean load (no pinch). How do those occur if there is no deformation?

I'm not trying to be a prick... just stating that it happens.

But the ball deforming is not important..... the ball moving at the point of contact of the air is what would cause spin. Using the glass barrel, put a dual colored ball in the barrel with the seam allinged perpendicular to the direction of travel (so if it spins the seam will look like a paddle wheel)... then hit it with the undershot bolt and see what happens.

Yes I know.. Tom Kay has the glass barrel. Lets get it from him and see.

E

I NEVER SAID THE BALL DOES NOT DEFORM

i said the ball does not deform due to the blast hitting it.

how many times do i have to post it?

dont believe me? look up the videos yourself "glass barrel" is a good search term.