Reliable testing the safety of paintball mortar ammo

[SEAR]

I already build a 2" ML mortar replica and I'm currently working on 60 mm M2 light mortar one. The projectiles are very light, soft and fragile on the tip and filled with marking powder. I'm not too far from testing top impacts on my head (with a mask on of course). What would you consider safe?

I mean most of us were already hit by a paintball or even FS round in the forehead or top of the head in an unfortunate situation and that hurts like a hell and leaves a bruise or a bump at least. What would you consider tolerable in case 51 mm or 60 mm mortar bomb accidentally hitting you from above? Similar pain level from a paintball hit ? No bruise ideally? What are your ideas for safety criteria?

[Ecapnation]

All depends on the fields liability

[BrickHaus]

It all comes down to how much energy is in the mass of a rocket when it hits the person I think.



I assume the rocket accelerates to apex, then turns, and falls to the forces of gravity. Its been a long time since Ive ran these kind of calculations. So Im going to graze over it as Ill likely mess up if I try to truly solve it.

E = 1/2 m v² (1)

where

E = kinetic (dynamic) energy (J, ft lb)

m = mass of the object (kg, slugs)

v = velocity of the object (m/s, ft/s)


I guess we could assume velocity at 9.8m/s² or 32ft/s²

Then plug the mass in and you at least have a perfect scenario energy to go off of.

But I compare that to the energy a paintball carries at 300fps. I think a paintball at muzzle velocity is 12.4 joules? ( fact check that plz) If your rockets carry more energy falling than a paintball does flying, Id say there will never be a safe scenario.


also in ANY situation, could it possibly carry enough energy to knock someones mask off? To validate that, Id set a mask up on a mannequin head, and dial your mortars into hitting it repeatedly. Can it knock the mask off? If it can, Id say the odds of " safely" launching these in crowds is dropping.

All in all, whats your goal here? To be able to use these mortars at commercial fields? Or just to validate you aren't goin to hurt someone at your field?

[SEAR]

Thank you, BrickHaus, for your insights! It is almost impossible to calculate the downward speed of a mortar bomb from reaching the apex. But by rough calculation 51 mm one should be very equal energy-wise to a full speed paintball, while 60 mm one could be a bit higher (more aerodynamic and longer effective range with similar weight). But the surface and energy distribution is not comparable to a paintball, it just behaves differently. I need to test it personally. I'm sure it will not knock the mask off - at least a mask without a shield (that is the only risk I foresee)

Field owners in my vicinity usually accept my test results (if I test my projects on myself) and I do my best to validate the safety of my heavy ordnance. So I'm looking primary to not to hurt someone on the fields where they accept my "toys".

[maggot]

But by rough calculation 51 mm one should be very equal energy-wise to a full speed paintball, while 60 mm one could be a bit higher (more aerodynamic and longer effective range with similar weight). But the surface and energy distribution is not comparable to a paintball, it just behaves differently. I need to test it personally. I'm sure it will not knock the mask off - at least a mask without a shield (that is the only risk I foresee)

Field owners in my vicinity usually accept my test results (if I test my projects on myself) and I do my best to validate the safety of my heavy ordnance. So I'm looking primary to not to hurt someone on the fields where they accept my "toys".

I think this falls into the category of "not a good idea", unless this is planned to be used with a very small group on a private field that everyone knows of it in advance. Our safety strategy relies on the premise that projectiles are coming at us horizontally, not raining down from above.
Just my $.02. Sounds like it would be fun to goof around with and play in the backyard though.

[XEMON]

I guess we could assume velocity at 9.8m/s² or 32ft/s²

well, that's your acceleration, not your velocity.

It is almost impossible to calculate the downward speed of a mortar bomb from reaching the apex.

Its your first college physic class ... if you know e few data point you will know when, where, at what speed and what is the impact energy of your projectile.

Do you know/can you share:
- projectile mass
- projectile initial velocity
- angle of the barrel
- range would help too

[BrickHaus]

Thanks X. I used to be able to crunch energy calcs in my sleep, but that was 10 years, and many many many beers ago. Haha.

[XEMON]

Honestly, im gonna have to take my old physic textbook 😅

[Siress]

kinematic equations are just napkin math, to be honest. It's definitely a starting point, though. There are tons of free calculators online or you can just read through the four primary 'kinematic equations' themselves.

The impact energy is just the kinetic energy; so 1/2*m*V^2 in units kg and m/s^2, resulting in units of Joules. For a paintball adhering to ASTM F1979-99 (the last version I have a copy of), the maximum kinetic energy permissible is 1/2*.0035kg*91.3 m/s^2 = 0.159 joules for a paintball. The complexity comes in when you consider that the impact energy of a paintball is largely redirected when the paintball shell breaks.

An interesting thing about safety is that it considers not just the intended target, but the unintended target(s) as well. Namely, the happy-go-lucky kid that runs in front of this mortar right as someone hits the trigger. There's no viable way around that issue unless you're launching it from a height that is 7ft above the tallest spot that a player can stand on the field. Even if you put a Cartman-COVID stick on it to keep people away in a sizable radius, the issue of potentially hitting someone at near-muzzle-velocity will still exist if they can be at a higher elevation. Ricochet shots are something to consider as well... Anyway, all of this is to say - you're not going to satisfy the safety wardens unless this thing is mounted on the window of the tallest tower, or if it's safe to hit someone point blank.

Let's get back to the numbers. Since the mortar has a fixed mass, let's back-calculate what the muzzle velocity could be if we do not exceed the energy of the paintball. According to Google, a Nerf football has a mass of 4.6 oz (=.130 kg). To have 0.159 J, we could launch that football up to a staggering... 5 FPS (1.56 m/s). So, what gives? How do we get away with launching Nerf footballs out of spud guns in scenario games? Great question. Please let me know if anyone finds out. My guess is, 'ask for forgiveness, not permission.'

[Axel]

Some guys just pick a random photo off the internet and call it an avatar, but you sir, have clearly earned the right to yours.

[Siress]

Redemption. https://www.mcarterbrown.com/forum/m...822#post276822

[Chuck E Ducky]

I feel like this is a question for ChatGPT lol

[Trbo323]

But the surface and energy distribution is not comparable to a paintball, it ".

Doesn't matter, ASTM testing doesn't care what surface it's impacting. Doing this by memory but if I remember right they really only care about the total energy because they basically assume a worst case scenario ie: your mortar round sat outside overnight in Alaska in winter and a polar bear named DocsMachine picked it up and fires it and it hits a kid named jinx on the top of the head.

It doesn't really matter what the "typical" situation is, you need to make sure jinx doesn't need an ambulance ride

Because I'm sure a ride in the polar bear's ambulance is more life threatening anyway

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[Siress]

But the surface and energy distribution is not comparable to a paintball

Doesn't matter, ASTM testing doesn't care what surface it's impacting.

That's very wrong. Those factors matter a great deal. And ASTM certainly do care. "...plywood target with a minimum thickness of 10-mm ..." - ASTM F1979-99, Standard Specification for Paintballs used in the sport of Paintball.

Just think of some scenarios in everyday life... A person can kick a soccer ball fast enough to give it ~300 joules of kinetic energy. If that struck you, you'd be annoyed. If someone put 300 joules into a ball bearing that struck you, you might die. That's roughly the kinetic energy of a typical .22LR. Again, kinematic equations are basically just napkin math... starting point only.

EDIT: I just realized, this topic is highly related to the text under my avatar. I hypothesize the highest density paintball permitted by the ASTM spec. will be the most accurate paintball. The smaller paint of today isn't necessarily a bad thing if they increase the density of the fill - though this says nothing about marking visibility.

[Trbo323]

That's very wrong. Those factors matter a great deal. And ASTM certainly do care. "...plywood target with a minimum thickness of 10-mm ..." - ASTM F1979-99, Standard Specification for Paintballs used in the sport of Paintball.
.

We are talking about two different things.

I'm saying on the field it doesn't matter what it impacts, it shouldn't be a danger, as in, assume worst case scenario, side/top of the head impact, maybe throat.

You are talking about the testing requirements which absolutely need something standard to measure against.

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[SEAR]

The impact energy is just the kinetic energy; so 1/2*m*V^2 in units kg and m/s^2, resulting in units of Joules. For a paintball adhering to ASTM F1979-99 (the last version I have a copy of), the maximum kinetic energy permissible is 1/2*.0035kg*91.3 m/s^2 = 0.159 joules for a paintball. The complexity comes in when you consider that the impact energy of a paintball is largely redirected when the paintball shell breaks.

An interesting thing about safety is that it considers not just the intended target, but the unintended target(s) as well. Namely, the happy-go-lucky kid that runs in front of this mortar right as someone hits the trigger.

Thanks for the advise! The safety during the launch will be handled by infrared sensors and receivers as on your typical old TV remote. No obstacle noticed within 1.5 m from the end of the barrel and it discharges.

[Siress]

Scope creep! haha Sounds like a really fun project.

[NONOBLITUS]

The stuff you have made in the past is so damn cool, looking forward to seeing this as well. You guys have some seriously great looking events and fields to play at.

[SEAR]

The stuff you have made in the past is so damn cool, looking forward to seeing this as well. You guys have some seriously great looking events and fields to play at.

Thank you for your kind words, man! We are still working on new WWII replica heavy weapons and on new games; but the market is just not too supportive. There are lots of folks in airsoft, but without paintball-grade masks our heavy weapons are no-go there.