What's a Joule?
- 1 LMAG Standards
- 2 Why are we measuring joules?
- 3 Additional References
Muzzle Velocity Limits and Minimum Engagement Distances
Example Weapons Measured with 0.20 g BBs
|Weapon||Muzzle Velocity Limit||Muzzle Energy Limit|
|CQB or Sidearm||330 ft/s||1 Joule|
|AEG Rifle||400||1.48 J|
|Designated Marksman Rifle||450||1.9 J|
|Certified Sniper||500||2.3 J|
Simple calculation for Muzzle Energy:
Kinetic Energy derivation:
Energy = 0.5 * mass (kg) * square of velocity (m/s)
For use, including factors for mixed units (g and ft/s)
Energy = [ Speed (fps) squared ] * BB mass (g) / 21500
(good for two decimal places)
eg. Energy = 400*400 * 0.20 / 21500 = 1.48 Joules
Why are we measuring joules?
Joules you idiots by Zach Billings
My biggest pet peeve in the airsoft world is the way that people talk about the power of a gun. The standard for measuring an airsoft gun’s power is to chronograph a 0.2g bb fired from the gun. This system is used throughout most of North America and the world for establishing field limits as well. A common limit for an outdoor airsoft field might be 400fps with 0.2g bbs. The field that I frequent has its limit set at 400fps (feet/second) with 0.25g bbs (0.25s being the less common standard for measurement). Why on Earth do we use velocity as a standard if bb weight is a variable?!
To give you a little background, this is how it works. I show up at the field with my airsoft rifle. I chronograph the gun using ammunition provided to me by the field, to ensure that no one cheats. I fire three rounds and so long as they all clock under 400fps with the supplied 0.25s, I pass. Then for the rest of the day I actually utilize 0.28 or 0.30g bbs. The additional weight of the bb decreases my velocity at the muzzle (the end of the barrel) but the energy carried by the bb remains a constant, at around 1.85J (Joules).
The point behind using a heavier bb is that they resist wind more. The heavier your bb, the less it’s effected by side to side wind and the more slowly it looses energy as it flies down-range.
People use a huge variety of bb weights in their guns. The light 0.2g bbs are usually reserved only for players who are not in-the-know. 0.25s are commonly used for pistols and less-powerful rifles. For players who understand bb flight characteristics and have a moderately powerful rifle, the weights used are 0.28, 0.30, 0.36, and 0.43 grams. 0.36 and 0.43 are usually [incorrectly] reserved for snipers.
Because every player actually plays will a different weight, it seems asinine to me that the standard for measurement is with a single bb weight at x velocity. Joules should be used as the standard, and velocity-with-weight would only be used for chronographing at the field.
The reason this came up is that I am a regular poster on Airsoft Retreat, and since I don’t use 0.2g bbs for any purpose, I don’t own any. Now, when I go to chronograph a gun at home to post information about it, I have to use results achieved with .25s. Most people don’t know how to convert these results and only understand velocity measurements given with 0.2g bbs. Lets inject a little science into the community and get a standardized system going!
Here’s some additional information on why I use heavier bbs (I will be using 0.36 or 0.43g this year).
Many players gripe about a heavier bb causing a lower muzzle velocity, but here’s the catch: Lets say I fire a 0.25 at 400fps. That’s about 1.85J. That means that a 0.43 fired from the same gun would leave the barrel at only 290fps. To most players this seems like a hinderance. Nay. Lets go 21m (69ft) down range. The 0.25 was greatly effected by the wind and has now slowed to 203fps. Meanwhile the 0.43, which started 110fps slower, is now traveling faster at 205fps. Most people with guns shooting above 1.6J are regularly engaging targets beyond 100ft. At those ranges, not only are the 0.43s now going faster, but they are carrying vastly more energy to continue their journey with. At the aforementioned 21 meters, the 0.25 has dropped from 1.85J at the muzzle to only 0.47J. The 0.43 has retained much more energy and is still carrying 0.84J of the original 1.85J.
There are tradeoffs involved which don’t always make heavier better. If you’re shooting at ranges beyond 50 meters then heavier is always better, because at 50m the average speed of all bb weights is about the same. If, however, you are engaging in urban combat at close ranges, you may want to stick to something like a .28. At a mere 12 meters, the .28 will reach its target more quickly and at that range you don’t need to be as concerned with conserving stored energy. You just want it to get there as immediately as possible.
This year I plan to carry a combination of 0.28s for close quarters use, and 0.36s for long range use.
Airsoft Energy Chart covering multiple ammunition masses.
Texas Airsoft Organization
These players set their limits based on Muzzle Energy:
- CQB = 0.83 Joule (300 ft/s for 0.2, 270 for 0.25, 250 for 0.28)
- Pistol = 1.13 Joule
- AR = 1.48 Joule
- Support Weapon (SAW) = 1.87 Joule (must have standard AR secondary weapon, MED 40 ft)
- Sniper = 2.81 Joule (includes DMR, gun with Full Auto capability prohibited and must have secondary weapon, MED 100 ft)
Buffalo Airsoft ( http://www.thewarstore.org )
Another reference that includes the Muzzle Energy as a key component in the gun classification. It is the only way to set limits on gun capacity that is independent of BB mass.
Canada Customs Practices ca 2012
Updated Customs practices for 28 February 2012:
- "Based on the latest research, it is now established that the muzzle velocity at which a .20g 6mm plastic airsoft projectile is capable of causing serious bodily injury is 111.6 m/s (366 fps). "
- For customs, "Airsoft guns, firing a .20g 6mm plastic pellet, with a muzzle velocity above 111.6 m/s (366 fps), will be classified as firearms. Please refer to D19-13-2 for the import requirements of low muzzle velocity firearms, including low muzzle velocity “uncontrolled” firearms. "
Learned discussion: http://www.airsoftcanada.com/showthread.php?t=137167
2012 Lower Mainland Universal FPS
Universal Muzzle Energy Limit ratified January 2012. Participating clubs: FVAA, BCAC, Op-For.
FOR PLAYERS USE
Each club will set the rules of engagement and the engagement distances. All participating clubs will honour the limits shown below.
Universal Energy Limits Specification wrote:
2. STANDARD LIMIT VALUES
|Gun Class||Muzzle Velocity (0.20g BB)||Muzzle Energy Equivalent|
|CQB or Sidearm||n/a||330||0||1.00 J|
|DMR (Sniper 1)||420||450||0||1.90|
- Tolerance only applies to settlement of newly installed springs and other mechanical modifications. Over long term, users are expected to ensure their guns achieve the limit on subsequent tests.
- Engagement distances are at the discretion of the member organizations.
- Sniper weapon class users are required to carry a secondary weapon in either the Sidearm or Automatic Electric Gun class.
- Muzzle energy for Sidearm and Close Quarters Battle weapons needs review to address improvements in available guns. Club admins reserve the right to meet and revise the velocity limit as determined after agreed review.
We will post a copy of the full document once its signature page is scanned and incorporated into the original.
Copy of ratified Universal FPS: http://mypage.uniserve.ca/~jneri/ex/mou-ufps-rev5-ratified.pdf