Paintball

[russc]

High pressure air can be pretty destructive. I've only ever seen one glass barrel video (The AGD one) and it was neither detailed nor particularly high framerate. [edit] Sorry, I've also seen the PPS video which is even less useful besides proving that they have a glass barrel.

[cockerpunk]

Originally Posted by russc

High pressure air can be pretty destructive. I've only ever seen one glass barrel video (The AGD one) and it was neither detailed nor particularly high framerate. [edit] Sorry, I've also seen the PPS video which is even less useful besides proving that they have a glass barrel.

i believe Simon posted on that is quite good. with his his speed camera.

[russc]

All I could find were his slow motion bolt movements and trigger pulls.

[agentSmith]

Tried to post this earlier but I was having internet problems, which turned out to result from my english setter chewing the cabletv cable off of the house. Pointers steal treats, English Setters steal cable!

Well, we agree on your data and many of your particulars until we get to magnus lift. I don't feel nor have I seen any data that can't(IMO) be explained by my theory of the operations of Vortex Shedding+Spin. Perhaps I missed the calculations that arrived at the possibility of magnus lift being generated, but in the AO thread the number arrived at was much higher, around 70,000rpm if I recall.
To me, it is the interaction of Vortex shedding and spin cancelling out those vortices that try to force a ball downward and assisting the vortices trying to push the ball upwards that is most likely to provide the majority of the lift, with the magnus effect which requires much more spin for action, being a small factor for only the first short piece of the trajectory, if at all.
Remember every foot the ball slows in the air AND the spin slows, it doesn't keep spinning at the same rate any more than it travels at the same rate. If magnus effect were the actor, then it seems you would see a ball that lifted at first, but at some point switched into a normal trajectory as the spin decreased. Instead the arc of the trajectories I see would seem to suggest lift continues even when there's not enough spin for magnus to operate. I wish there was some way to measure the RPM at 100'. I wonder if a handheld remote tachometer would read such a small object.

Like Fubarius, I think in terms of stories not statistics.
A ball is resting against the bolt face. Air enters the Better Bolt from the bottom, some taking a hard turn and traveling down the bottom of the bolt and the rest moving up to the middle of the bolt before turning to impact the ball. Air hits the bottom edge of the ball at roughly the same time as the center. The column of air at the center pushes into the ball starting it on it's way and breaking it free of all static friction, as the column of air at the bottom hits the seam. If the seam is parallel to the bolt face, then spin is applied in a perfect vertical axis. If the seam is skewed, one part of the seam will be impacted first and start a nonvertical spin, air catching the rest of the seam will try to correct the rotation to the vertical. This would explain the odd effects of greater inaccuracy, inconsistent spin and lift as nonvertical spin will not produce an equal amount of lift. Energy used to create nonvertical spin is lost as the air against the seams attempts to align the ball vertically and so less spin AND less velocity. The rest of the travel down the barrel is immaterial(except as increased friction slows the spin)

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

I was referring to the seam pulling the rest of the ball into an egg shape as it is accelerated by the air at a greater rate than the smooth sides of the ball would be, but not something that needs to be severe enough to be visible. The ball will not resist the pull of the seam(with the seam like the sail on a boat), especially with another column of air striking the center of the ball to help, otherwise it would,IMO, rip the ball in half. I wish there was a way to trap the ball and let the bolts rip them apart in such a way that we could look at the pieces.

Rob

[drg]

Originally Posted by agentSmith

A ball is resting against the bolt face. Air enters the Better Bolt from the bottom, some taking a hard turn and traveling down the bottom of the bolt and the rest moving up to the middle of the bolt before turning to impact the ball. Air hits the bottom edge of the ball at roughly the same time as the center. The column of air at the center pushes into the ball starting it on it's way and breaking it free of all static friction, as the column of air at the bottom hits the seam.

FWIW the better bolt doesn't have a center hole, just a rectangular port at the bottom of the bolt.

[agentSmith]

I'll look again this weekend but I could swear... AH well, I'll be doing field studies with my P68SC all weekend at the Monster Game!!! I'll make sure!


Rob

[brycelarson]

I think that the idea of seam alignment is prob a valid suggestion. The cooper T had a slightly higher standard deviation on both the X and Y values out of the matched barrel. This indicates to me that it's somehow being effected by the seam.

The three bolts that we tested at .687 lined up like this:

Venturi - most consistent in X, CP's backspin bolt 2nd and the cooper was the least consistent in the X axis.

the mean impact location for the three was in the same order - the venturi being the lowest, CP's backspin bolt in the middle and Cooper the highest. We can't actually claim that his bolt worked - it ALMOST statistically worked, but wasn't a large enough increase to claim.

So, my theory is based on the seam. I suggest that the ball gets some spin - but only when firmly held in the path of the air flow. The magnitude of this spin and the direction is created by the location of the seam. In the cases that the seam is vertical - then the spin is vertical. This gives a little more rotation and get the slightly higher impact location.

In the case of the overbore barrel - there isn't enough friction to hold the ball in place for the force to be concentrated on the bottom of the ball. As soon as the air flow enters the breech the ball moves away from the bolt and the air flow equalizes in the whole chamber.

As both CP and I have stated in the past - the bottom line of out testing is always usefulness in play. 2" at 50' just isn't enough to make this a really useful tool. I'm sure that it's possible that there may be greater impact on certain conditions - ball to barrel match, seam alignment, air flow rate etc. - but I think that any improvement in vertical trajectory will be accompanied by greater variability in the X axis as well. So, a perfectly tuned cooper setup may give some increase in range, but at the expense of the grouping size left to right - a poor trade off I think - and one that seems to hold true for other ball spin systems.

[drg]

Originally Posted by brycelarson

So, a perfectly tuned cooper setup may give some increase in range, but at the expense of the grouping size left to right - a poor trade off I think - and one that seems to hold true for other ball spin systems.

Yet those systems sell .... so it can't truly be written off.

Going back to the seam thing, I wonder if a ball had multiple seams or .. dammit ... dimples, if it would work better.

[brycelarson]

Originally Posted by drg

Yet those systems sell .... so it can't truly be written off.

Going back to the seam thing, I wonder if a ball had multiple seams or .. dammit ... dimples, if it would work better.

well just because something sells doesn't mean it's good - nor does it mean it's effective. However, most of the flatline / apex guys tend to like to dump paint. You know - the 14 pod mil-sim scenario guy who shoots 3 cases a day of play. I'm not knocking them - if they like playing that way - and are willing to put a hopper into a bush 250' away because they think a guy might be in there - then the flatline / apex is a perfect tool for them. And if they're having fun and giving me a chance to shoot them with my pump - then it's great for everyone. However, I've been at the receiving end of long range backspin shooting - and you don't usually have to dodge too many shots if you just stand still - and those that you do have to move away from are going really, really slow.

as for changing the ball to increase the effect - yes, I'm sure that there are many ways to make the ball catch more spin. The golf ball is symmetrical on tons of axes (I think that's plural of axis - right?), which reduces the inconsistencies produced by spin.

I think we can all agree that there are vastly more effective projectiles than paintballs.

[cockerpunk]

Originally Posted by drg

Yet those systems sell .....

so did the pet rock