Paintball

[brycelarson]

Originally Posted by agentSmith

It has been my experience that the single biggest factor affecting the flight of balls from my Cooper-T is the orientation of the seam, that's why I like it in the Sheridan where I can see the ball fall into the bore. It gives me a reliable clue to where in the band of possible trajectory a particular shot will fall.

this was one of our conversations - and certainly not something we could control for using a hopper fed sniper.....

[agentSmith]

Nor was I suggesting you should Bryce, since real world applicability for someone named CockerPunk would require a Cocker.

It is a factor though, that I feel can explain variations in data.

If it was a true paint to barrel match.. would the paint move at all?

I think Schmitti meant spin, but if the ball will slide down the barrel, it will theoretically spin inside the barrel. Being able to shoot .687 into a .679 bore without breakage also suggests that my theory of BIGtime deformation of the ball at the moment of underspin air impact is at least possible.

Rob

[brycelarson]

Originally Posted by agentSmith

It is a factor though, that I feel can explain variations in data.

and it's certainly something CP and I discussed.

[cockerpunk]

Originally Posted by agentSmith

The ball, held more tightly in the sized bore, would put up more resistance to the initial impact of the air and feel the effect of the pressure imbalance more effectively than a looser ball that simply started moving the instant any air hit it.

ah, that is a good idea ...

Originally Posted by Schmitti

If you punch a vertical board at the bottom, the entire board moves... just the bottom (point of impact) first. THe base of the ball, point of impact reacts first. You don't get instantaneous oressure equalization... close but not immediate.

but a fluid does not act the same as a contact force. it would be more along the lines of hitting a beachball with a water hose.

Originally Posted by agentSmith

Being able to shoot .687 into a .679 bore without breakage also suggests that my theory of BIGtime deformation of the ball at the moment of underspin air impact is at least possible.

Rob

unfortuntly that is simply not true. numorous high speed videos of paintballs in glass barrels show that the ball does nto deform from the air blast.

[Schmitti]

I think Schmitti meant spin

Nope... I meant what I said... just a very generalized statement to make people think.... and you did.

but a fluid does not act the same as a contact force. it would be more along the lines of hitting a beachball with a water hose.

So instead push a ballon filled with a cherry slushy.... push it at the bottom... it slides, but you get deflection as the ballon resists movement at first because of surface friction and not wanting to move. Push it at the top (un restrained side) and it will roll.

I think issolated impact force at any point will certainly affect the way the ball moves, even if the paint to barrel match is perfect. Now will that effect be extreme or negligent because of the fact that is a deformable projectile?

I'm not trying to disprove your theory or the tests. I think both are very good. I could do with out the statistics language as it reminds me too much of struggling through that class when it was taught by a 60 year old professor from India that you couldn't understand... even when he was reading word for word from the book. But it seems to be good work.

E

[agentSmith]

Well if deformation of the ball doesn't give the mass of air purchase against the ball, then I'm even more convinced that the increased pressure catches the seams to spin the ball. That would explain my other observations too, I guess.

Rob

[HP_Lovecraft]

Originally Posted by agentSmith

then I'm even more convinced that the increased pressure catches the seams to spin the ball. That would explain my other observations too, I guess.

Thats interesting. For 15 years, I assumed the spin orientation determined how much magnus was produced.

Schmitti is the expert, but in order to generate a magnus force, the projectile needs to disturb the airflow. IE baseballs need the seam, and golf balls need the dimples, otherwise no magnus. The orientation of the seam of a paintball is problematic since it only follows a single axis, meaning that the amount of magnus generated is variable, relative to rotational degree of that axis.

At least, that was always my view. I figured the spin itself was constant, but the magnus was variable. But it looks like the spin itself might be variable as well, due to the way the pressure grabs the seam?

Unfortunetly, this area is fairly subject to conjecture, as there is no direct way to measure this.

The only real way to measure the spin is to use my ballistic charts out to a range of 50-100 feet. We know how much height different we should see.

Then we can test hand-feeding differnet paintballs of different seam orientation, barrel lengths, and barrel IDs?

[cockerpunk]

Originally Posted by Schmitti

So instead push a ballon filled with a cherry slushy.... push it at the bottom... it slides, but you get deflection as the ballon resists movement at first because of surface friction and not wanting to move. Push it at the top (un restrained side) and it will roll.

well, TK showed that the fill rotated with the ball, and the glass barrel experiments showed that the ball does not deform when hit by the air pulse.

im sticking with the beachball and water hose, or perhaps a ridgid waterballon filled with water and an air hose.

the seams is something i brought up with bryce, and it might be a contributig factor, but the sad thing is the list of minor contributing factors seems to be growing, and the big one IMO, is the paintball itself. again, i think our paint to barrel match testing holds IMO what is happening here.

[Schmitti]

Easy now.... 12 plus credits of Engineering Mechanics, that many of physics and anothe 20 some in engineering that had physics and free body diagrams doesn't make me "the expert"

Thanks for the vote of confidence though.

In theory (and this is what makes it really frickin hard because it's three dimensional with forces acting all over the god damn place) it looks like if you hit the bottom with the blast of air you will get some rotation of the ball prior to the ball moving down the barrel.... how much rotation? That I don't know. It all happens very fast. If you could keep the gas away from acting on the rest of the ball you would possibly get more rotation.

Anyways.... I just got a call about fixing my chimney.. so I'm going to go close my hand in a filing cabinet a couple times as it might hurt more than the cost of this chimney repair.

E

[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