First Strike Test Series, Part 2: Action Type and Accuracy

A semi-formal data driven analysis of paintball’s leading shaped projectile. I know its been awhile since my last test release but there were some trials and tribulations between here and there, check out the link if you’re interested in the meta-process that goes into ensuring quality data.

Contents

  1. Intro and Manufacturing Consistency
  2. Action Type and Accuracy

The What, Why, and Before

Do the forces involved in a paintball markers internal firing cycle affect First Strike accuracy? We know that in the real steel world it does, in fact, make a difference. As a general holistic trend, the accuracy of a firearm scales with the magnitude of forces involved in it’s firing cycle. For example, compare the accuracy expected of a bolt-action sniper rifle to that of a sub-machine gun.

But in general paintball its been (rightly) accepted that these forces do not play a significant role in a marker’s accuracy. Paintball’s technical community has found that either the forces involved are too small to negatively affect the projectile or the inherent inaccuracy of a paintball is so great that any minor added error from forceful firing cycles is lost in practical testing. Either way, the end result is the same; it doesn’t seem to matter what kind of marker you use. At least with conventional ammunition.

First Strikes are much much more accurate than classical spherical paintballs. It stands to reason then, that any added error from a forceful firing cycle has a greater chance of manifesting in a measurable way. The signal is much less likely to be lost in the ammo’s “noise”. Furthermore any additional error in FS accuracy will matter more than with classical ammo since the round itself and the playing style typical of shaped ammo is much more dependent on that accuracy for it’s kills (and cost-per-kill). With First Strikes it both easier and more critical to find out if there is any added error from the marker’s action.

Before we move on, lets make note of some technical considerations. First, the action is the mechanism by which a marker loads, fires, and recocks. Typically a marker loads a round from the open or closed bolt position, fires it with some variation of poppet or spool valve, and recocks in an autoloading capacity or manually. Open bolt guns feed, fire, and then recock in that order. Closed bolt guns fire, recock, and then feed. The advantage of which, at least in the real steel world, is that there is less potentially disruptive motion in the gun before the round is released. Poppet valves tend to accelerate rounds faster than spoolies (hence their efficiency) but are also known for the kick that this produces. Auto-loading (semi-automatic or automatic) guns likewise experience more movement when firing than manual/pump guns.

Secondly, ‘force’ in the preceding and the following, refers to the holistic forces experienced by a given marker during its firing cycle. Specifically, from the time that the trigger is pulled to the moment the round exits the muzzle. For example, in open bolt auto-loading guns this would mean the sum forces experienced by the gun during chambering, striking the valve, and the simultaneous acceleration of both the round and the action. Note that since action type is how we’re measuring force in this experiment (lacking more sophisticated means), I sometimes use the terms interchangeably.

The Numbers

Da numbers.

Methodology and Interpretation

With the previously discussed action types there are eight possible configurations of marker. For practical reasons not every variation was tested since some configurations are difficult to acquire, redundant in terms of the forces they experience, and/or less applicable to the paintball community as a whole. Instead, three marker configurations were used to bracket the range of forces from highest, to middling, to least. For the highest force, we fired an old school Spyder – an open bolt semi-auto poppet. For the middling force we used the data produced by Punkworks in their FS rifled barrel test for the Tiberius T9, an open bolt semi-auto spoolie. For the lowest force we used a closed bolt pump spoolie in the form of an Empire Trracer that was graciously provided by scotallen1986 for use in this test series.

Note that the Punkworks results are qualified with an equal to or greater than symbol. The limitations of their firing platform resulted in shifting points of aim for each eight round magazine. These groups were then mathematically corrected and centered on the same point. The math used to do this, however, can damp out some of the natural randomness in the rounds. Generally, the larger the dispersion the more exaggerated the improvement. In small dispersions the improvement is minor or non-existent. Since the final value is relatively small, I’m confident that it’s close to what the value would have been, had their magazine not forced a shift in the point of aim. If anyone is interested in the specifics of the math I’ll post up some previous testing runs and walk through the proof for the above generality.

The test was conducted in an indoor un-airconditioned range. Specifically, the newly acquired first floor warehouse of the local hacker/maker space JaxHax. The distance from gun to target was 75 feet and the gun was clamped firmly by the firing table. Our rounds were ratioed according to the average size distribution found in theManufacturing Consistency test and both the Spyder and the Trracer were regulated by a Palmer’s Stabilzer. The impacts were recorded on a 1” x 1” grid so the final position of the hits were rounded to the nearest whole number, unless they fell directly between two grid lines in which case they were recorded at the half simply because I didn’t like the existential dilemma of having to round a perfect split. Previously, we’ve run tests down to a resolution of 0.1 inches but as it turned out, that amount of accuracy did not produce different final results from a 1 inch resolution – it was also a massive pain in the ***.

For the open bolt poppet and the closed bolt poppet (the Spyder and Trracer respectively) each round was loaded into the breech and pushed forward past the breech by hand. This was done for two practical reasons, the markers did not have magazines that could feed rounds into them, and more importantly, it prevented the bolts from damaging the skirts and influencing accuracy. The Spyder MR5 (a mag fed gun) we used earlier in testing would occasionally do this; though, since we were using an early run barrel adapter, I cant say that it was due to a design flaw in the MR5 itself.

A laser was mounted to each marker and projected onto the wall behind the target. A mark was then taped to the wall to indicate the original point of aim of the marker. The mark and laser point were compared after firing to ensure that they occupied the same point. Since any shift in the markers orientation during firing would cause the laser to move off the reference point, by doing this, we were able to ensure that the point of aim remained constant throughout firing.

As for the accuracy metric (the means by which we measure accuracy), I’ve included both x-component standard deviation and vectors. If you’re unfamiliar with those terms, the x-component refers to the amount of left-right dispersion that a given group suffers from, and standard deviation is a statistical method for measuring how wide that dispersion is. If that didn’t help much, here’s a link that explains standard deviation. Vector is the most popular method for measuring accuracy in paintball. It combines the x and y component standard deviations into a single radius that can be used to model accuracy as a circle, similar to how some first person shooters model the accuracy of different in-game guns. If that didn’t help, heres a link that explains vector in more detail. Personally, for reasons explained here, I prefer using the X-component standard deviation.

Hammerhead rifled barrels were used for each test. The high and low force markers used the exact same barrel, and the medium force marker used a model specifically designed for the T9. The key barrel specs in each case are the same: 0.688 bore and a 1:52 twist rate.

Thoughts and Conclusions

Ladies and gentlemen: we saw noticeable improvements in accuracy as we stepped towards the low force gun.

The difference between the highest force marker and the lowest force marker is especially stark. An X-component standard deviation of about 1.3 for our lowest and 2.7 from our highest. More than double. Consistent with the trend, the middling marker falls between the two – though its interesting to note how much it leans towards the lower end.

But why the change? What causes our softer markers to be more accurate than the more forceful one? Originally the only thing I suspected was barrel flex. Which is to say that the intensity of the markers action was causing the barrel to flex inconsistently during firing. Classic barrel harmonics. This arose from some early testing with First Strike spin rate where I used a high speed camera to try and count the number of revolutions that the round made in a given number of high speed frames in order to determine it’s exit RPM (an attempt at measuring twist-rate slippage). It didn’t work, but it did capture some high speed video showing the surprising amount of barrel flex that goes on in an open-bolt poppet. Here’s a video I made at the time where we can compare the flex of the barrel in free-floated and then braced positions. Watch carefully for barrel movement before and after the round has exited the muzzle.

The contrast is plain. So this is likely a prime contender for the accuracy changes we’re seeing. The other possibility, which only occurs to me because the two spool valves are a lot closer in performance than the two open bolts, is that the manner of acceleration may have something to do with it. Poppet valves typically use a a sudden and forceful kick of air to accelerate the projectile. Its part of what makes them so efficient. Spool valves, on the other hand tend to accelerate the round more gradually. It could be that that gradual acceleration is better for rifling engagement. The stronger kick of the poppet could be causing the round to slip some of the rifling, giving it sub-optimal stabilization, or causing it to shear slightly against the lands and grooves (which would likewise cause sub-optimal stabilization). It could also be that the similarity in performance is simply due to larger than expected compensation by the mathematical method used to make it. Unfortunately, I don’t think we’ll know the full dynamic here for a while yet. The means by which it could be easily tested are beyond us and the difficulty of testing it with the means we do have put it low on our list of resource-to-merit return questions.

Update: As cockerpunk pointed out, the Traccer is in fact a variation of the poppet valve. Its such a light weight, low kick action that I never even considered that it could be a poppet. Seriously, it kicks like baby hiccups. Now our final results show that our middle and low force marker tiers are close to each for reasons that arent likely due to their acceleration curves. Thus, I’m retracting the acceleration part of the theory and adding weight to the barrel-flex/action-force theory. Especially considering that our middle and low force markers (the two that were relatively close in performance) where both linear actions, meaning that their forces were symmetrical and inline with the barrel, and our worst performer was the stacked tube blow-back, a marker with large asymmetric forces working off axis with the barrel. This is something that we might be able to get more info on with somehigh speed camera testing.

Update: A finite element analysis (a kind of computer aided simulation) conducted by Lurker27 on a common barrel form, found that the deflection necessary to reach the outer edge of our largest group required only 0.53 mm, or about 0.021 inches. Also be sure to check out Lurker Paintball. They were some of the first to explicitly incorporate Punkworks’ findings into their designs. +1 for forward thinking and market pro-active paintball companies.

Either way, it looks like the kind of marker you shoot First Strikes with does indeed makes a difference. In the FS community, this is a sentiment that echoes those of notable first strike shooter jjron and of some Carmatech SAR12 users that purchased semi-auto engines for their marker. For now, if you’re jumping into the long range mag-fed game (and, lets be real, you should be) get something with a little less oomph in its action. If you’re already toting around a long range death machine (and the the body count that comes with it), use the settings that get you less oomph.

Closing Notes

Its necessary to say that what we saw here today could be a fluke. Thats’ part of the reason why you post your method and data. So that the rest of the technical community can check you work and repeat your tests. With the sample sizes we shot it’s statistically unlikely, but in the interest of full disclosure, it bears mentioning.

Also Be sure to take a look at my about page for the thank you’s and acknowledgements, it’s worth the jump.

Finally, one things in closing. If you’re technically minded and you see some aspect of the data or argument that can be improved, feel free to drop me a PM or post. Self-initiated and community driven edits are expected to be ongoing. [Several have already been incorporated]

Thank you for reading, and I don’t know when we’ll drop the next test but it will probably feature sorted paint and centrifuge settled ammo (centrifuged to encourage symmetrical distribution of mass). Be on the lookout.

Expansions—————————————————————–

Quote:
Originally Posted by brycelarson (of Punkworks)

Here’s what a vector of 8.5 v 2.5 looks like:

First set – 16″ Lapco smooth bore – 16 shots. Second set – 16″ Lapco rifled – 24 shots.

Barrel Flex Analysis Done by Lurker27 (of Lurker Paintball fame):

Quote:
Originally Posted by Lurker27 View Post
[…]Now, we can make an estimate with a model of a typical barrel,. what kind of force does it take to produce that deflection? I am using a 14″ Eigenbarrel v1 one piece in my Finite Element Analysis here. So, the angle will be defined by:

deflection/length = tan(.0015) = .0015

.0015*14 inches=0.021 inches (about 1/3 the thickness of an o-ring)

Or, 0.53 mm tip deflection.

I then varied the force applied to the Eigenbarrel FEA to get roughly this displacement.

[…]

Barrel Flex Examples

Quote:
Originally Posted by Whiskey Hammer View Post
Barrel Flex in a High Force Marker (0:00):

Barrel Flex in a Lower Force Marker (0:45):

General Accuracy Comparison, Including Paintballs Modeled at 75 Ft

On Rigidity of the Mounting System and More on Flex

Quote:
Originally Posted by Whiskey Hammer View Post

[…] The first is at 10,000 FPS and uses a clamped setup. Watch the barrel not the muzzle. Despite no apparent movement in the frame/body of the marker, the barrel whips around like a pool noodle. Also note, in the second slower replay, the barrel is moving before, and as, the ball exits the muzzle.

[…] In short, despite significantly more stabilization than what a human can generate, we saw noticeable barrel movement. And then we saw it again, and again, and again, and again.

So far we have five videos showing barrel movement, proof that the force required is relatively mild, and not only a direct precedent set under parallel physical circumstances, but a result consistent with the precedent. Is it possible that its all a fluke? Sure. Like Lurker said, its great to check and to question. But at this point, with the robust body of evidence we have, barrel harmonics is where the moneyball is.

Update: The rigidity thing came up elsewhere as well but in the form of a more focused question, since it’s relevent I’ll mirror the answer here: “The differences between the groups would only become zero as themounting system approached perfect rigidity if the barrel were also perfectly rigid. […]Even if the inaccuracy were solely due to imperfect rigidity in the mounting system, the accuracy trend would still extend through less rigid platforms, the delta would just scale with the flex in the system and a human operator could still expect relatively more accuracy in low force systems than high force systems.”

10,000 Frames Per Second Hammer Head Footage (0:00)

≥2,500 Frames Per Second (4:56)

You can find the community discussion of this post at the following forums:

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