Monday, 9 May 2022

Engineering - Paintballs

This is a short story about an 'aha' moment... sometimes you read something and it makes things make sense... this is one of those.

So two weekends ago [at time I originally laid down this article] I played paintball for the first time in over a decade (yes, it's monumentally sad when you can measure things in decades) and while the resultant limping during the start of the subsequent week was annoying, it was totally worth it.

Being in the bush, the mechanics of the markers, the sun and sky... all worth it.

Then what?

Being interested in this activity for a while I'd read some of 'the more keen' stuff... and I knew of course that paintballs are wildly inaccurate. Everyone knows this. You can see it. There are no paintball snipers. Not really - not in regular ol paintball... arguments re First Strike not withstanding.

[aside: first strike rounds (pic above) have a half-sphere with paint inside and a back end kind of resembling a bullet. I've seen slow-mo of them in flight actually spinning like a bullet (which is weird given the liquid aspect) i'm sure regular drag probably has as a substantial effect as well (i.e. like a dart).]

From a ballistics point of view it makes sense right? They're balls. Musket balls were more inaccurate than 'proper' bullets which could be spun with rifling to provide higher accuracy.

But in this case the issue is more fundamental than the shape of the projectile.

There are innumerable commentaries re accuracy that discuss barrel diameter vs paintball calibre... co2 vs hpa... how the air escapes the barrel / porting... open bolt vs closed bolt... different valve types this and that...

Found it...

"Can someone explain to me why longer barrels don't increase accuracy?"

https://www.reddit.com/r/paintball/comments/3bcamn/can_someone_explain_to_me_why_longer_barrels_dont/

"But that's a moot point anyway, because paintballs are imperfect spheroids with a liquid filling. They're just such shitty projectiles that anything a barrel might do is lost in the random noise due to the paintballs themselves. Basically, if the barrel is long enough to get them up to velocity and point in a straight line (apex/flatline not withstanding) that's all it can do."

...

"The better question is, why WOULD a longer barrel lead to more accuracy?"

"Because longer barrels increase muzzle velocity by focussing the force for longer. Markers have restricted muzzle velocities."

...

"It's spherical, half filled with liquid, and often times have imperfections such has dimples and an oil coating. I remember someone describing a paintball to me like a water balloon half filled with water, you can't really throw it accurately."

And that right there was the moment.

Paintballs cannot be 'accurate' simple because they are (semi-)filled with liquid.

While the air pressure and acceleration on the ball are able to get the ball moving 'enough' to impart general 'directioness', that fluid element rules out actual accuracy.

I have no doubt that I could throw an apple more accurately than I could throw a water balloon. A solid just naturally doesn't have the (obvious) extra internal forces affecting its flight path.

Aside ramblings...

Similarly, there was one story about a plane crashing in south america (from memory - no sources to be provided) where someone had bought an alligator onto the plane and everyone rushed to the back to get away from it, tilting the plane sufficiently off axis for it to crash.

Back into it...

Markers have a fixed limit on the power they're allowed to deliver - projectiles travel no faster than 300fps. There is therefore a very limited range, a clearly visible parabolic flight path, and sometimes the ability to even get out of the way. Leaves, winds or even rain drops can effect these light-weight projectiles.

Given the nature of paintballs it's surprising they can even slightly resemble accuracy.

However, in a way they can, over the distances required. And it is a matter of mimicking accuracy with an adjacent property: consistency.

The machining and tolerances on modern equipment is(/can be) quite exceptional now days. So the barrel diameter and ultimately the power delivered by the valves etc can be exceptionally repeatable. Similarly paint can be good or bad too, and apparently high quality paint is consistently round which does help it fly straighter.

Within those parameters it is possible with good equipment and good paint to get the equipment to produce repeatable trajectories and (more apparently accurate) resultant group placements.

But that's about as good as it gets...

Aiming in paintball is mainly about sending a few shots and adjusting subsequent shots to where the paint indicates it's going. There's little point having iron sights, let alone a red dot or scope other than as a cool accessory... we're talking 30 meters maximum effective range here (yes you can lob them on a higher arc - and they'll probably bounce - this isn't a debate re the technicalities).

So who cares...

It's not just a matter of "oh that's interesting". It's a matter of that new knowledge  a) potentially stops one buying gizmos that proclaim increased accuracy (if one is so inclined to such purchases), and more importantly   b) understanding the nature of the projectile/mechanical system helps one to manage the expectations. 

You are not going to get 'accurate' paint. But you can possibly achieve a smaller zone or spread with a given group of shots.

It's not a matter of the knowledge making you more accurate (which is not possible). It's a matter of using that new information to practice techniques to become more consistent (or even upgrading your kit to help with that possibility).

Anyway, just something that got me thinking.

Until next time...


Some time (days/weeks) later...

So I was talking to the guy at the paintball shop over the road (yes, I actually have a paintball shop over the road. How freakin cool is that?!). Discussing equipment and whatnot, in specific to the topic above... barrel kits.

The (where to start)... barrels that come with 'low end' guns are designed to allow you to shoot paint from whatever field you play out. Specifically, some fields have (very slightly) larger paintball, some smaller. So the barrels provided with these ('hire-gun intended' markers) are made larger to allow 'all' paint to fit through.

If you have your own marker and buy i.e. a box of paint at the field you can change inserts within the barrel to fix the size of the paint you just got (on the assumption that all the balls in the box are of a homogenous size).

[pic (example kit): the colour bits are barrel inserts of various diameters. the smallest black piece is the bit that the insert is put into - the 'outer barrel'. Then one of the two extenders (on the left) are screwed onto the outer barrel. 
So only the colour part is used for 'power generation' - and given there a fixed limit the balls can travel at it doesn't need to be much.
Most barrels now days have lots of holes (porting). This is used to a) [mainly] dissipate the sound of the shot sideways (or not just out of the end of the barrel), and b) [theoretically] allow the air to escape from behind the ball quickly and in multiple directions once it exits the 'power tube' so as not to effect its path further (reduce turbulence).]

So you get your paintball, put it on top of the opening of the insert (the specifically bored cylinder) and if the ball rolls through easily it's too big. Repeat the process with a smaller (diameter) insert until the ball just sits on top or just inside the barrel (i.e. it doesn't roll all the way through). If you can then blow the ball through (like a blowgun) without an excessive exhalation then it's the right size. Repeat the test with a few sample balls from the batch to work out the most appropriate insert for your paint.   

If the barrel is too tight then you get more ball breakages on the way out.

And back to why this is somewhat relevant to the topic... if it's too loose the ball can bounce up and down as it moves down the tube which doesn't aid 'accuracy', and could impart spin on the ball. Additionally (and probably more importantly really), a lot more air passes around the ball, meaning more air is required to get it up to legit speed, which meaning you go through a tank of air quicker. So it's more efficient to have a better fit.

Again, the term 'accuracy' is a stand in for consistent, but every little bit helps, and I wasn't about to open up that can of worms with the paintball shop owner.

Do you need them? No. Is it nice(/more consistent/more efficient) to have? Yes.

[LATER 2024-08-06...

turns out that 'common' insert kits come in two length; approximately 5" and 8".  and apparently the 8" one is 'optimal' for purpose.]


Until next time...


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