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130FPS Ballistic Limit
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Boff
The Dealer


Joined: 08 Dec 2012
Posts: 3391
Fav. Blaster: (Modified) Stampede ECS
Location: Bristol, UK



Post 130FPS Ballistic Limit  Reply with quote
I guess 130FPS as the UK standard probably originates from my post with Green Cloaks on ballistic limits. As far as I know, it was the first codified rule set for ballistic limits in the UK and has been adopted by several organisers as a standard. Here I'll walk through how I arrived at the limit and why it's important for a LARP context. I'll also comment on current and prospective UK legislation and how that will influence, any changes game organisers might want to implement.

First considerations:
The most important consideration for a LARP system is that it's an open field system with up to 14 hours of play in some areas. Wearing eye protection for that period is often uncomfortable and next to impossible to enforce so it needs to be borne in mind that people won't always be wearing it.

Kinetic Energy & Kinetic Energy Density:
A dart in flight uses kinetic energy to keep flying. The energy it has imparted to it by the launcher (i.e. your blaster) and it is a function of mass and velocity. The equation is as follows:

KE = 1/2m * v^2 where KE = Kinetic Energy (J), m = mass (kg), v = velocity (m/s)

Kinetic energy density is much more difficult to calculate but it's very important to understand. Essentially, it's the amount of kinetic energy per unit area of impact. It's based on the KE of the projectile, the properties of the impact surface and the area of that surface.

Kinetic Energy and Your Eye:
I studied Virology & Immunology at University and one of the areas that includes is ocular immunopathology - i.e. diseases of the eye, including opthalmias originating from trauma. Eye injuries for metallic spheres start at 0.8J (I can find the paper if anyone is interested). At 0.8J you're looking at perhaps a 50% chance of an eye injury that will require hospital treatment. That's hospital treatment, mind - it doesn't cover blindess and other permenant vision changes which have a much lower chance of at 0.8J. Bear in mind, that's for a metal projectile similar to a ball bearing.

Further, this doesn't account for Kinetic Energy Density, however. With most darts, you have a springy, soft topped head which prevents a 100% transfer of energy between the dart and your eye. Some of it is lost in compression of the tip like a car's crumple zone. We had to do some guesswork here to work out which darts had enough 'springiness' to be used with the system and what KE we could go up to. Compression is based on the Young's Modulus and other properties of a material that we don't currently have the equipment to measure. I think Doom over on Nerf Haven has a full protocol for doing that but we've not gotten around to it. It's on the list and we'll get to it eventually.

The 1J Limit:
We opted for a 1J limit since the tips of most darts are springy enough to dissipate a good chunk of impact energy and have a large area to reduce the impact force. Voberries and FVJs obviously don't have the necessary compression to manage that so require a lower limit.



I put the above chart together for the thread on the Police and Crime Bill (PCB) but it's also useful here to visualise the 1J limit as it stands. For most commonly used projectiles, 130FPS is where the 1J line lies. Note that I have over-stated the weight of Koosh darts for legacy reasons, current Generation 3 Koosh weigh around 1g-1.05g.

Ammunition choices:
For Green Cloaks, Voberries are banned out right partly because of their lack of compression and the fact they're overweight. Getting a Voberry to chronograph requires a much more powerful launcher than Koosh or Elites. I proved that hefting Voberries is a nightmare in my ballistic work back in March of 2015. For other game organisers, using 110FPS or 120FPS as a cap when firing Voberries across the chronograph would provide a more open ammunition policy. For Green Cloaks, however, the number of welts and general unpleasantness in a more open game means we ban them outright.

Displacement and range choices:
Ballistic limits of course influence game design and mechanics. 130FPS means that from a 1.5m firing height, you're looking at around 72ft of absolute range. Travel time for that is around 2s which is plenty of time to dodge so higher muzzle velocities can be used to reduce that time to target. The close in effective range of Nerf projectiles is what makes them a desirable combat type alternative to airsoft or paintball as the games are much faster paced and closer in terms of action.

Ballistic limits and the law:
Current UK legislation and statutory instruments suggest that 1.3J for FA and 2.5J for SA are fine for airsoft. Those numbers were provided by the Forensic Science Service. However, the Firearms Consultative Committee in its Eleventh Annual Report and the Law Commission in December 2015 suggested the 1J limit. That in turn is being implemented in the upcoming Police and Crime bill which has been discussed on this forum. The most up to date advice from the Home Office can be found here - see Section 2.4. It's not known yet if flywheel blasters will be covered by this legislation as they are not barrelled nor do they rely on compressed gas. Work is ongoing to get a legal opinion on this.

Assuming the 1.3J and 2.5J limits for airsoft stand then the following is true for fully automatic fire:

Original image for reference

2.5J for semi-automatic fire:

Original image for reference

And if the 1J limit is enforced then you'll be looking the at chart first referenced above.

Alterations and further notes:
Of course, the design of the Green Cloaks is within the parameters of that system. The 1J/130FPS limit has been adopted by other game organisers as it can protect fixtures and fittings in indoor settings from damage and the like. It is up to individual game organisers to produce their own sets of guidelines and ensure they publish them openly for people to build to. I've already mentioned that Voberries could be admitted to a system if all blasters are tested on them and a lower muzzle velocity is used which may act as a proxy for a higher velocity in a lighter projectile. There are other considerations and changes that can be made to the system. For example, short, highly supervised games, non-compressible tips such as FVJs would be feasible provided all personnel are wearing eye protection.

Final word:
The key, above everything else, is to have the limits openly published so attendees can work the them. The worst thing in the world is to have pain tests or other subjective, flaky tests that create friction between attendees and organisers. I will be recommending the 1J/130FPS standard be maintained as the UK standard for now. Until we can guarantee that a flywheel system will not breach the new PCB limits when it becomes law next year, I wouldn't want to be recommending anything else.

Ultimately, the old mantra applies: 90% player, 10% hardware. We can sit here and throw around shiny toys but if you don't watch your corners, can't reload worth a damn and can't move at pace then you're going to get nommed or tagged out. Smile

I'll be happy to take any questions and generally offer advice. I hope the above offers some insight into my thinking and how it all works.

_________________
Boff: Managing Director, Blastersmiths UK & BUZAN Founder (formerly)
| Blog: nerfarmourer.tumblr.com | Website: www.blastersmiths.co.uk | Legal: http://pastebin.com/6sQ7c3jg |

Last edited by Boff on Tue Oct 25, 2016 8:51 am; edited 1 time in total
Sat Sep 03, 2016 8:08 pm View user's profile Send private message Visit poster's website
OldNoob
Foam Data Collector


Joined: 07 May 2013
Posts: 4833
Fav. Blaster: Xtreme 180 Rapidstrike
Location: In the Boonies



Post Reply with quote
Thanks for this, now stickied. With discussion on the 1j limit etc it's pertinent.

_________________
Big_Poppa_Nerf wrote:

Boff whats the damage? I have spent over 3 times my Nerf budget this month already. Part of me is trying to be a responsible parent/husband/house owner. The other half is just says 'Ahhhh, Screw it!'.
Sat Sep 03, 2016 9:21 pm View user's profile Send private message Send e-mail
L11
Game Organiser


Joined: 20 May 2016
Posts: 238
Fav. Blaster: Tri-Hellcat Rapidstrike
Location: Newport, S.Wales



Post Reply with quote
This was a really good read, thanks.
Sat Sep 03, 2016 9:45 pm View user's profile Send private message
Justin Andrews
Junior Member


Joined: 16 Jun 2016
Posts: 20
Location: Leicester



Post Reply with quote
I'd like to add, since the amendment is now in for Airsoft guns, that the exception only applies to ammunition which is a small (6-8mm) plastic pellet :


Quote:
“57A Exception for airsoft guns

(2) An “airsoft gun” is a barrelled weapon of any description from which
only a small plastic missile, with kinetic energy at the muzzle of the
weapon that does not exceed the permitted level, can be discharged.
(3) “Small plastic missile” means a missile that—
(a) is made wholly or partly from plastics, and
(b) does not exceed 6 millimetres in diameter. *


(*note this may be increased to 8mm)

This means the airsoft exemption is unlikely to apply to Nerf and Nerf like blasters.
Tue Dec 13, 2016 11:00 am View user's profile Send private message
Boff
The Dealer


Joined: 08 Dec 2012
Posts: 3391
Fav. Blaster: (Modified) Stampede ECS
Location: Bristol, UK



Post Reply with quote
You are correct that the exemption will not apply to air powered Nerf blasters. The current working opinion from my legal team is that flywheel blasters will be fine because they're neither air/gas powered nor are they barrelled. That's a working opinion, however.

It's worth stressing that the new PCB changes will mean very little for public Nerf insofar as we don't usually go much above 130 with Elites anyway. Anything that does consistently fire above that limit using air power will be considered an air weapon and would be treated like an air rifle would be (i.e. proper storage, no use on public land, no use within 50ft of the centre of a highway etc).

_________________
Boff: Managing Director, Blastersmiths UK & BUZAN Founder (formerly)
| Blog: nerfarmourer.tumblr.com | Website: www.blastersmiths.co.uk | Legal: http://pastebin.com/6sQ7c3jg |
Tue Dec 13, 2016 11:31 am View user's profile Send private message Visit poster's website
UK Foam
Regular Member


Joined: 27 Sep 2015
Posts: 215
Fav. Blaster: Stryfe / Apollo
Location: Bristol / Bath



Post Reply with quote
This all checks out with me; however, what about rival ammunition? These have a different mass, so what is the fps limit for these?

A 130 fps dart seems to hurt a lot less than a 130fps rival ball.

Thanks

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Wed Dec 21, 2016 9:18 pm View user's profile Send private message Visit poster's website
OldNoob
Foam Data Collector


Joined: 07 May 2013
Posts: 4833
Fav. Blaster: Xtreme 180 Rapidstrike
Location: In the Boonies



Post Reply with quote
The KE for Rival rounds is on the data sheet, look at the last two lines.



_________________
Big_Poppa_Nerf wrote:

Boff whats the damage? I have spent over 3 times my Nerf budget this month already. Part of me is trying to be a responsible parent/husband/house owner. The other half is just says 'Ahhhh, Screw it!'.
Wed Dec 21, 2016 10:01 pm View user's profile Send private message Send e-mail
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