Wednesday, May 13, 2015

High Velocity BoomCo First Test Shots: Fail

So I got back to Site B and commenced the initial tests of the slick-coated BoomCo darts.

First of all, the barrel stock:

K&S 9319 - 1/2 OD x 0.035 wall aluminum tubing, .430 bore.

Perfect for use with the BoomCo dart and a pneumatic engine. Slightly smaller bore than the .436 provided by 15/32x0.014 (thin wall brass and aluminum). You can just see the slightest daylight around the widest part of the dart which is where the body is roll-crimped onto the tip.

This stuff is also a lot nicer to work with than the thin wall tubing. It is a lot like the .527x5/8" stuff used for .50 cal, just smaller.

I picked up a 3 foot stick of it, which I did not modify - because I now plan to return it.

This is the test gun, a PVC "mini spudgun" with a 150cm^3 chamber and a 1/2" port piston valve. The valve performance is excellent, similar to a QEV. This thing is more than equal to any sane use of a 4B tank even at sub-50psi pressures.

I didn't bother with the pressure gauge yet. Or the chrono, because I was an idiot and left it at Site A. However, I varied the pressure and velocity quite a bit during the test. I never went beyond about 40psi (12 strokes of the hand pump that I used).

Here is a sample of what I shot.

The shortened darts had the rolled-in end restored with a lighter.

Good news first: The coated tips work. There were no problems with the tips, darts sticking in the barrel, or consistency. As far as the internal ballistic aspect, everything was great.

Now for the bad. The main problem is that none of the darts were stable. The backstop I was shooting at was about 60 feet away (I never moved on to the longer ranges). Full length and shortened, they all acted up, and at any velocity. As soon as I got past "low-end-superstockish" (or, more practically, got up high enough to shoot flattish at this range), they began acting like elites and veering or describing a 2-4' wide spiral or erratic path, then hitting nowhere near where I was aiming. Tentatively, the shortened darts were the worst.

Perhaps that could be resolved with better barrel length tuning or porting, but experience tells me that projectiles requiring the like tend to be impractical and inferior to those that can tolerate some blast, like most .50 cal short darts.

Now this was the killer flaw:

On impact, most of these full-length darts (all of the above are, or were, unmodified length; dart on left for comparison) collapsed as shown.

The plastic tube tends to continue by inertia. The area where it is rolled down into the cannelures of the tip core is a weak spot and it tends to fold over itself in this manner.

This expands the dart, making it no longer fit in the barrel it was fired from.

The deformation is reasonably permanent. Straightening the dart after this is difficult and getting it to fit as it did originally impossible.

While most darts won't hit a wood fence like these, many do hit harder parts of gear and players as well as trees, walls and cover. And this was from 60 odd feet out, and while I don't have the chrono handy, most of these were not going over 300FPS. This is not acceptable for an expensive dart to fail in such an insidious manner, such that you might pick these up and have them not feed.

Well, that's that.

At least I hope my barrel stock and tip mod info can help someone. Perhaps if you are looking for something superstock, or other than a stefan-competitor, you may like BoomCo, but I am not too impressed and will not go ahead with this venture.


  1. I rebarreled an air warriors extreme blastzooka to fire BOOMco darts as well. I was experience the same dart cumple you've shown here and was just about to post it.

    I'm likely going to continue using it as the darts I've put superglue I will not be using in clips ever again. My barrel setup was a small length of 7/16'' brass tube nestled inside a 1/2'' brass tube. The darts slide down the 1/2'' barrel and usually slip themselves into the 7/16'' barrel. It fits in the inner barrel up to the tip.

    I did not experience an unstable flight patterns during my testing. I may not have been getting the same velocities you were but my shots were predictable straight. I plan to continue turning the XBZ into a tac rail attachment.

  2. I salute you for even trying. I suspect both centre of mass and to a lesser extent tip aerodynamics are the cause of your flight problems. What is the tip weight to dart tube weight balance like? Typically in Nerf it's a 0.3g foam with a 0.7-1g tip.

  3. Cut the tips off where the ridges starts and fill the front end it hot glue. I've done hot glue tips with the ridges and they work pretty well in standard boomco. Not sure what would happen, but it may work, or it may crack the darts on impact. There's always a way, if there's a will.

    1. Anything of that sort creates what is legally a stefan, being non-manufactured, even "in spirit" (a homebrew molded rubber tip/tubular foam commercial style dart would be an example of that).

      It wasn't my intent here to explore handmade projectiles based on the plastic tube body concept. I do see this as a possible development area but there are concerns of standards compliance and game legality as well as litter when compared to .50 caliber foam body darts.

  4. I've been doing research on darts for use in a double stack magazine for a holsterable automatic nerf sidearm I'm working on.

    Many posts on reddit (and some blog posts) led me to believe that BOOMco darts have superior stability to nerf-style silicone-tipped foam darts because their center of gravity is further forward. However, when I started looking up actual specs, I found that modern nerf darts have about 2/3rds of their mass in the tip, but BOOMco darts only have about 1/3rd of their mass in the tip. This contradicted the common wisdom that dart stability is largely dependent on the center of gravity of the dart. Until I saw this blog post of yours, however, I had no evidence either way. It's undoubted that BOOMco darts exhibit high accuracy at their usual velocities, but I haven't seen much testing of their high-velocity behavior.

    The results of your testing bring BOOMco dart performance in line with new nerf's common wisdom about center of gravity and dart stability, but the reason for the instability is still in question. I wanted to know if you have any thoughts on that, or solutions? Is there a flaw in the profile of boomco darts, or inherent issues with the body or tip material or shape? Was it something to do with your modifications to the tip?

    What can I do to make a 30mm long or less dart exhibit acceptable stability and accuracy at sidearm engagement range?

    I'm defining sidearm engagement range as the distance at which it makes more sense to draw your sidearm than to change a mag, assuming sidearm draw is 0.2s to 0.5s and magazine change is 1s to 2s. That makes max sidearm range when the nearest threat is 1.8s away, which is a bit outside of Tueller drill time. Assume your zombie is a world-record sprinter, and they could cross seventeen meters in that time. Now, that's actually nearing the lower range limit of Hasbro darts out of super stock blasters. The sidearm ideally should be able to hit a human-sized target reliably at that range aiming flat, meaning the darts need to be stable across their whole flight path at super stock velocities.

    I'm currently designing and building a prototype for the blaster in question (and my printer really needs some work and I am considering replacing it or at least adding a second one), so I won't be able to work on the magazine for a few days and probably won't be able to do dart testing or design for a few weeks. I AM currently looking at what commercially available materials are purchasable in small quantities for development of the dart body and what techniques and designs are affordable in tip construction.

    Do you think the performance I'm looking for is achievable with short (30mm total length) soft tipped (but not tacky like 'smart stick') straw-body darts out of smooth thin wall metal tube like you tested above, or do I need to be looking elsewhere with the dart design right now? Is the standard wisdom about center of gravity and stability correct?

    Porting the barrel and better tuning of barrel length and diameter is absolutely an option and I will be looking into it (I *will* be trying to minimize blast in the short barrel I'm going to be working with), but you're absolutely right that a dart with robust behavior across a range of setups is strongly preferable to one that only works great in certain blasters as they are off the shelf and completely fails if you shorten or extend the barrel, drop your blaster in the mud and jam a port, do cosmetic mods that cover the ports, or various other things that can happen intentionally or otherwise.

    Stuff like optimized barrels should be like going from 'service rifle' to 'competition rifle' with firearms.