Sunday, September 29, 2013

Boring ballistics stuff. Chrono data, dart aging, RapidPistol, Z90 Redux.

Today I ran some more stuff over the clock.

First up: the Splatmaster Z90 got retested with Elites loaded all the way to the breech end of the barrel.

In the previous test of the Z90, all darts were loaded with the tip flush with the muzzle to produce a fair comparison with Sonics and Elites. I figured I would give it another go with Elites pushed back about 3/4" farther. Honestly, I didn't know what would happen to velocity and consistency, but I'm glad I tested that! It turns out that dead volume has a massive effect on these small-displacement springers and the 3/4" of pushback is worth 10-20 fps! Now we are pulling over 120fps with elites. Not shabby, and more in the same league as a good NF now.

Second, the RapidPistol got its test, finally.

Note a few things.

One, I have standardized the chrono data spreadsheet format, added some basic statistics (standard deviation, min/max and extreme spread) to make consistency and practical performance more apparent and foolproof than just the mean and the list of shots, and get more in line with how Foamdata Services and the like are reporting data. I also standardized the sample size for a normal test to 16 shots and will try to avoid throwing a random few rounds over the chrono and calling that a real test. It's not large enough for over the top statistical analysis, but it communicates quite well how the gun behaves and is enough certainty for what we are doing here.

Two, for flywheel guns, I have began recording the pack voltages at the beginning and end of each test. Fully charging the pack before a session does not remove the change in voltage during discharge, which is not negligible during a 100+ round chrono session, so this is better quantified in case some use or relation of that voltage data comes up that could call into question the integrity of the chrono data. Also, the energy consumption of a gun becomes apparent when the resting voltage of a Li-ion pack is monitored, and this will be useful as a rough estimate of battery life.

Three, new darts were tested against equivalents that have been in service for a decent time and would still be considered fit for use by my standards of the past. This was in response to this post by infamous and azrael at BNBS. While I have long known about significant negative effects on ballistic performance as darts age, accumulate normal wear and damage, lose the original foam dimensions and stiffness and gain defects, I honestly never knew how bad it was, and I have never bothered to test it. Infamous had posted some chrono numbers from a stock Retaliator that didn't seem to make sense, and I had commented something about that on reddit... but on further investigation they encountered a massive discrepancy in velocity between used and unfired darts.

Thus, I will be investigating foam degradation further. Here, I have completed the flywheel portion with this RapidPistol with shocking results - brand new darts, through flywheels, produce SIGNIFICANTLY more velocity than darts that have been mildly degraded and would still have been judged not just usable, but equivalent to new dart performance, in the past by visual and fit inspection!

Furthermore, I caught a flywheel-related wear mechanism that I don't think has ever been noticed before - when fired from some types of flywheel guns, the flywheel slip as the dart is grabbed results in wear of the foam near the front end of the dart behind the tip.

Such wear can eventually cause flat spots or a uniform reduction of diameter, visible as a "blunting" of the sharp cut edge of the foam, and this has a SERIOUS velocity effect. Several unexplainable low-velocity shots occurred which led to this finding (and were discarded after finding the anomalous darts, pending a test of exclusively worn darts culled from my dart supply to quantify the effect of this wear).

I also completed a "stockish" springer test with an AR'd Strongarm. There is a definite difference between new darts and used darts, even those that seem perfectly fine to any practical inspection! Seriously, if you are in some kind of competitive environment, ALWAYS RUN NEW DARTS! It's not a small edge you gain, it's massive. Trust me, I have the most stringent standards for darts during HvZ season of practically anyone and THAT is my baseline to which I compare new darts in these tests so if you simply cull worn-out darts YOU ARE NOT IMMUNE TO DART WEAR. ALWAYS USE BRAND NEW DARTS WHEN IT MATTERS! Also, these T-code Elites have uniformly had unreal performance. That warrants yet more testing. Perhaps code shopping is about to get reignited!

Still to come are a "pro stock" test with a heavily sprung Retal and Triad, and a test with pneumatic and spring guns with cylindrical barrels - convenient at the moment are my trusty SSPB attachment and my Z90 Splatmaster. In addition, I will be performing an aging test, involving the repeated firing and handling of said darts in a manner consistent with use, so as to create some kind of understanding of service life.


  1. Good idea! I probably create bigger samples than I need to but I wanted to be sure the crated spreadsheets were useful. I think there is some very interesting info to be dug out with proper testing, thanks for putting these up.

  2. Regarding used darts, something that I brought out before was splitting - when a dart is fired with such power (springers only) that the foam can't take all the pressure and splits along the edge. As a result, firing these split darts out of spring operated guns results in a dramatic decrease in performance. Flywheels do not seem to have as much of a problem with this splitting as they're just flinging darts out.

    1. A split foam is a major defect, and I guess it's assumed and understood that you don't try to fire a split foam. That's like driving on a flat tire. Hence I will not be investigating this.

      The cause of split foam is overly high muzzle pressure due to poor barrel design, not some arbitrary barrier of energy/velocity/chamber pressure. High-energy guns are frequent offenders for foam shredding since their optimal barrel lengths are longer than expected and often ignored. 100% of these cases can be corrected with the proper barrel (even my 660cc piston valve cannon at 60 psi will not burst or shred a recycled K code foam with a 4 foot barrel as is called for).

  3. Perhaps you can do something to increase the life of your darts, I put a dab of glue on the inside of my dart and rotate a plastic straw down till it hits the tip, then when the glue dries I cut the extra straw off.
    This straw would help counteract the pressures of the flywheels and push the foam back a little bit when they get gripped by the wheels.
    This also prevents darts from getting squished while in some of the larger clips, since doing this I have had very very few jams in my flywheel blasters.
    This does not work for blasters with pegs for obvious reasons.

    For my own curiosity, what is the life cycle of the new dart performance, is it literally the first time it has been shot or does it have 4 or 5 shots till its performance decreases?

    1. The "straw mod" has been around for years. I have never really bothered with it, since the foam wearout is mainly not deformation, but actual breakdown of the foam cell structure (and in the case of flywheels, the foam near the tip being ground and melted away completely). Crushed darts are rarely a problem for me, since any dart old enough to crush or bend in normal use is already garbage for other reasons.

      For cylindrical barrels, like the ones we make from pipe/tubing, I suspect the straw method is more worthwhile (since these barrels are less sensitive to foam diameter and darts may be usable longer) but there may also be a significant problem caused by a rigid object inside foam as it is fired from a long barrel. Old Streamlines and their rubber core come to mind - Elites have much more consistent and better performance from long barrels. Complex matter of necessary foam compression on pressurization.

      Perhaps I ought to test it in flywheels, though, because the reinforcement effect of putting something inside the foam might improve flywheel contact pressure enough to affect velocity. Good call.

      About the life cycle of darts, I did conduct a test of the ZombieStrike Elite which contained 10 firings of these with various guns. By rotating the initial guns back in from time to time, a loss of velocity was observed, and I can confirm that degradation is always happening from the first shot. Pure firing and reloading, though, is not a large impact even with flywheels and a 150fps NF mixed in - I was seeing less than 1 fps loss on the Strongarm per 5 shots (shooting darts over the chrono into a backstop, picking them up and reusing them). It's the other aspects of use that do the damage, and those are difficult to quantify.

  4. In the tubes barrels it might be better for them considering the uniform compression (I don't have a good model to base this on though). If the straw were properly glued and bonded to the inside of the foam it would help resist the compression.

    I would love to see both types fired through a clear tube with a slow motion camera to see this foam compression.

    Scientific ramblings (just me thinking out loud and giving others a chance to see what I'm thinking about)
    If the foam compresses does it compress out or in.
    if the foam compresses out it would create a better seal between the dart and the tube.
    If the foam compresses in it would make the dart contact the sides less and the air escaping between the foam and the tube would create a sort of slip stream that the dart could ride on and drastically reduce friction.
    when does the dart decompress, in doing so does it have a sort of spring effect, does the dart head push the foam back into spot or does the foam propel the head forward...

    Can we get myth busters on this.

    1. The foam compression I am referring to is hydrostatic (uniform). Every dimension shrinks. You can visualize by putting a piece of FBR in a sealed syringe and pushing the plunger and watching it crush.

      As to resisting it, the compression is necessary. Nerf darts have internal ballistics as efficient as they do because of it. Without it, the friction force acting on a dart when firing it would be equal to the friction force you can observe while ramrodding a dart through a barrel - which can be several pounds of force for some springers. This would be horrendously inefficient. A solid incompressible projectile and barrel combo with the same characteristics (normal force, contact area, coefficient of friction) as a nerf dart would be impossible. It is because the foam "releases" the bore and has very little force acting between it and the bore, and thus has very little friction, that nerf darts even work as a projectile for an airgun.

      Clear barrels are an interesting idea, but the compression will not (always) be visible, since it is slight and most of it is going into undoing the "preload" caused by forcing an oversize foam into a barrel, so the foam will not actually change dimensions.

      Perhaps initially with a high-pressure airgun with a fast valve there would be a definite crushing.

    2. I see, that was a very thought provoking answer and very finalizing not much more to discuss for dart compression lol.

      If you get around to testing the straw mod I would love to see the results, maybe you can think of some more things to put inside the darts.