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Dimensionally stable skirmishing projectiles

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Dimensionally stable skirmishing projectiles

Unread postAuthor: Zeus » Mon Jan 14, 2013 10:20 pm

I've been employed to design and make a few different sorts of airsoft gun, and the obvious limitation of airsoft is the projectile. BBs are easy to feed, and cheap to buy, but even heavy BBs are useless past 250'.

So I considered for an AMR style launcher, a better projectile should be made. I'm working around a single shot case action (you need to give it some disadvantage) using coaxial cartridges. I'm looking at a 10mm bore, and similar dimensions to most .50BMG rifles.

The projectiles need to be safe, cheap to produce, reasonably accurate (12MOA is doable, 6 would be ideal), and fit a 10mm bore. Cast hot glue in a mold, with a hollow tail set into the base would be my first thought.

Any suggestions? I'm working on the math for safe projectiles at the moment, my source is from this thread.
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Unread postAuthor: Lockednloaded » Mon Jan 14, 2013 10:27 pm

RAP4 makes a fin stabilized airsoft projectile that may suit your needs
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 15, 2013 1:31 am

Lockednloaded wrote:RAP4 makes a fin stabilized airsoft projectile that may suit your needs


These were the first that came to mind but at 6mm diameter and 0.19 grams weight, they still have a very poor sectional density which means they will likely not be much better than spherical BBs.

I had done some GGDT modelling here showing the differences in range from improving the drag coefficient and improving the sectional density.

First, the drag coefficient is incrementally reduced:

Image

Next, drag coefficient is kept constant but projectile diameter is reduced, while keeping the same weight, thus increasing sectional density:

Image

GGDT simulations using a 20 gram projectile in a 1 inch barrel fired at high subsonic velocity. In one series I varied the drag coefficient, in the other the projectile diameter (1 inch -> 0.5 inch -> 0.25 inch -> 0.125 inch), in all cases the velocity and weight was kept constant.


I doubt the RAP4 projectiles would fare much better than say simply using a 0.43g spherical BB.

I don't think upping the bore to 10mm would be helpful either in view of the above.

I would favour a "foster slug" type projectile as you were considering:

Image

I don't know if hot glue would be the best material to cast them out of though, perhaps you should look into silicone casting? A durable material means they're less likely to come apart in the barrel, and perhaps they could be re-used if recovered.

Still, hitting anything further than 100 metres or so would seem like a bit of a stretch if you're limited to "safe" velocities...
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Unread postAuthor: Zeus » Tue Jan 15, 2013 4:06 am

jackssmirkingrevenge wrote:
Lockednloaded wrote:RAP4 makes a fin stabilized airsoft projectile that may suit your needs


These were the first that came to mind but at 6mm diameter and 0.19 grams weight, they still have a very poor sectional density which means they will likely not be much better than spherical BBs.



My thoughts exactly, the Airfin is a clever idea poorly implemented. If it were made to a similar density as .43 BBs, then it might have some value.


jackssmirkingrevenge wrote:I don't think upping the bore to 10mm would be helpful either in view of the above.

I would favour a "foster slug" type projectile as you were considering:

I don't know if hot glue would be the best material to cast them out of though, perhaps you should look into silicone casting? A durable material means they're less likely to come apart in the barrel, and perhaps they could be re-used if recovered.

Still, hitting anything further than 100 metres or so would seem like a bit of a stretch if you're limited to "safe" velocities...


The advantages behind a larger bore is the capability of heavier projectiles, without resorting to doping the projectile with powdered metal, which is a pain in the arse.

I plan to play with foster slugs, and a plain slug with a lightweight tail.

Hot glue is incredibly cheap, but caulking silicone seemsto be ideal, I'll look into it further.

The people I skirmish with are mainly military or ex military, so we just wear full face protection, and use the harden the fork up principle. But this would have a minimum engagement distance, you wouldn't sneak up and use an AMR from 200 meters, so why would you use it at 20 meters in airsoft.

I've found that with the guns we play with (tuned up AEGs and springers, and the odd GBB), it's generally scaleable by a factor of 10, so a run of the mill AEG tops out at 40 meters, which matches an assault rifle being roughly accurate to 400. Which is why I'd like this accurate to 150-200 meters, to match a .50BMG and the like.

I do have near unlimited quantities of cheap telescoping tubing, in 10mm OD, 12mm, 14mm, 16mm 18mm and 20mm, all with 1mm walls. If I can stay within those sizes, I can reduce the cost by quite an amount, and make $700 instead of $550 from making one.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 15, 2013 4:33 am

Zeus wrote:The advantages behind a larger bore is the capability of heavier projectiles, without resorting to doping the projectile with powdered metal, which is a pain in the arse.


Ah, but you could always make it longer. Here's a firearm example with one modern and one classic cartridge:

Image

Image

Both fire a slug of similar weight with high subsonic velocity. The sectional density of the 300 blackout is much higher though, and the shape more aerodynamic. Which do you think makes the better long range round?

I think if William Godfray de Lisle had been able to get his hands on the latter round, there would have been no contest :)

Image

*fap fap fap fap fap*

Have you thought of adding silicone to a length of drinking straw for example? A "kinder" version of this:

Image

The proportions and balance means it will fly straight no problem:

Image
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Unread postAuthor: Zeus » Tue Jan 15, 2013 5:13 am

True, I'm not aiming for compatibility between my launcher and standard airsoft guns (even the Wingun 701 I use would barely give it a flick, and it shoots 450 fps with .25g BBs), so there's nothing tying me to 6mm, and the larger the surface area, the less penetration, which makes it somewhat safer at higher power.

My main concern is wind susceptibility, it's not a concern at short range, but a projectile with such a light tail would surely be affected more than a .50BMG over the scaled range. I could rifle the barrel, but that's added complexity, and maths that I can't really do.

On the topic of the thread you reference, all things going well I'll have a reasonably capable lathe in my possesion within two months or so, and if I find work in the mean time, I'll invest in a very capable lathe instead

So with the permission of my gun friendly neighbors, I'll have a 2 mile long range, 350 acres all up, and if I get my other neighbors in on it, I'll have 650 acres to find such a projectile. I've got a 1/2" QEV set up at the minute, and a 3/4" coming in within the month. With any luck, I'll have a lot of hard data on projectile stability and geometry.
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Unread postAuthor: PVC Arsenal 17 » Tue Jan 15, 2013 8:43 am

I would look into .410 shotshell wads (unslit is best) and possibly bullet sabots. Though depending on what you're doing with this, 250'+ and stability against wind seem to imply that this wouldn't be a toy anymore. Careful...
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 15, 2013 9:20 am

Zeus wrote:and the larger the surface area, the less penetration, which makes it somewhat safer at higher power.


Bit of a catch 22 here, because when a projectile is "safe", ie doesn't penetrate the target, then it probably has the sort of features (low density, blunt shape, low velocity etc.) that make it very bad at "penetrating" the air, meaning it will slow down rapidly and have the trajectory of a mortar.

My main concern is wind susceptibility, it's not a concern at short range, but a projectile with such a light tail would surely be affected more than a .50BMG over the scaled range. I could rifle the barrel, but that's added complexity, and maths that I can't really do.


Weathercocking is a problem with rockets too: http://www.grc.nasa.gov/WWW/k-12/rocket/rktcock.html

If you're going for a drag stabilised projectile, it's something you're going to have to contend with.

Because of the safety issue, there's a limit to how much you can improve projectile performance, so the solution in my view is to go for consistency, and to know how the projectile reacts to range and wind, then adjust aim accordingly.

With a marginal projectile, range estimation is critical. Something like this won't break the bank and will give you the data and precision you need: http://www.ebay.com/itm/NEW-Wildgame-In ... 53f3122b1f

I would compliment it with a cheap anemometer: http://www.ebay.com/itm/NEW-DIGITAL-HAN ... 3a6599d831

Once you have your system, test the crap out of it. Set up range markers at 5 metre intervals and establish projectile drop, and combine it with a low magnification mildot scope.

I don't see any other way to consistently hit a man sized target at 200 metres with such a low spec projectile unless this "homework" is carried out.

I've got a 1/2" QEV set up at the minute, and a 3/4" coming in within the month. With any luck, I'll have a lot of hard data on projectile stability and geometry.


Sounds promising :) I bet you could go for the whole two miles with some careful projectile design.

PVC Arsenal 17 wrote:I would look into .410 shotshell wads (unslit is best) and possibly bullet sabots. Though depending on what you're doing with this, 250'+ and stability against wind seem to imply that this wouldn't be a toy anymore. Careful...


You mean use the wads themselves as projectiles, fired back to front?
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Unread postAuthor: al-xg » Tue Jan 15, 2013 9:32 am

Just use an air rifle?

If you're concerned that's not safe, then less dense projectiles will just have to be used and you'll have to drop the range.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 15, 2013 9:39 am

al-xg wrote:Just use an air rifle?


Apparently how the SAS trained in the Malaysian jungle, with fencing masks for protection :)
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Unread postAuthor: PVC Arsenal 17 » Tue Jan 15, 2013 11:21 am

jackssmirkingrevenge wrote:
PVC Arsenal 17 wrote:I would look into .410 shotshell wads (unslit is best) and possibly bullet sabots. Though depending on what you're doing with this, 250'+ and stability against wind seem to imply that this wouldn't be a toy anymore. Careful...


You mean use the wads themselves as projectiles, fired back to front?


Correct, I've gotten good results from 20 and 28 ga wads. 20 ga fits perfectly in 1/2" sch40 PVC. I recommend unslit wads because the release of air at the muzzle tends to spread the "petals" apart creating all sorts of drag and instability. But if you tape them, they fire like lasers.

The cup-shaped piston end (normally the back) should be filled with hot glue and this forms the tip of the projectile.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 15, 2013 12:24 pm

Theyre not going to reach out so the sort of ranges Zeus is after though, unless fired like a howitzer.

As far as physics is concerned, I would say:

1) Safe
2) Long range
3) Practical accuracy

Pick any 2.

Realistically I would find it hard to hit a man sized target consistently shooting 16 grain lead pellets at 900 fps from my Monsoon at 200 yards.

According to Chairgun, at a 200 yard zero the pellet would rise 4 feet from the boreline, and with just 1 mph wind 90 degrees to the bore would drift 6 inches.

Energy on impact would be just under 6 ft lbs, definitely not "safe". It would also take just over a second to reach the target.
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Unread postAuthor: wyz2285 » Tue Jan 15, 2013 12:41 pm

I remember seen a similar discussion on an air soft forum, apparently safety made these more aerodynamic rounds unlikely to be used in field action. Personally I have tried to glue a short section of a straw on a bb, made the trajectory straighter but can't be used in a air soft gun, also no hop up effect.
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Unread postAuthor: PVC Arsenal 17 » Tue Jan 15, 2013 1:50 pm

Why not just use scenario paintball guns then?
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Unread postAuthor: Zeus » Wed Jan 16, 2013 4:18 am

Well, working my way up.

PVC, unfortunately scenario paintball guns aren't an option, they've got the same range as airsoft, and are far harder to import.

Wyz, that's exactly why I'm using a customized system, with a separate calibre to avoid confusion.

JSR, as I've said, we can set engagement distances, so something that might be dangerous at 20 meters, can be used safely at 100, and being shot at point blank with a 450fps .25g BB redefines pain, and paintballs have never come close to it. And we considered making Simunitions at one point, but that was discarded, not for the level of power, but convenience.

I will need to get a massive amount of hard data, and I can enter it into a smartphone based ballistics calcuatlor, which should simplify the entire process.
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