New SR-25s weapons from Specna Arms in stock! Get your own DMR!

How to measure power correctly

Tips & tricks HPA system Review

For a very long time there have been discussions about how to properly measure the performance of replicas. With the advent of HPA-powered replicas, this topic has become even more hotly debated. Our most knowledgeable lead service technician, who has over a decade of experience as an independent player and as one of the most respected technicians in the country, decided to write up how it actually works. Many thanks to Racek of RacekCustomGuns for a very well written article on the performance issues of airsoft replicas.

How to measure power correctly

Have a nice day, everybody.  Today let's take a look at a slightly longer article regarding performance limits at events, gun measurements and the difference between AEG and HPA.

Limits on events - what do we mean by this and what parameters do they actually limit?

Personally I'm very glad for the limits on events, I remember the times when power was absolutely not a concern, so you could easily have 1J and 4J players in combat at the same time. The difference in range and play style was enormous.

Thanks to the limits, we have an upper limit on the power for the action, so it makes the game more balanced and personally, more fun.  I would also like to mention that the power limits are purely a voluntary thing of the airsoft community and the organizers, as airsoft guns of category D are not restricted by law.

The limit can be used to restrict several parameters according to the space and thus adapt the game to the size of the space, limit the risk of injury, etc.

  • The first and simplest limit is on the muzzle velocity of the gun, in the vast majority measured at 0.20g. This method of measurement is now obsolete due to joule creep, it can commonly happen that despite the limit in place there are people on the field with much higher power.
  • The second limit is on the kinetic energy of the BB. Compared to the velocity, this limit already accounts for the higher weight of the balls and therefore also for joule creep. Of course, the measurement is based on the ammunition the player is shooting with or on the maximum allowed weight of the course.
  • The third is the firing mode limit. Full auto is not needed everywhere and could lead to a higher likelihood of injury, especially on CQB fields. So one can limit the firing modes, whether semi only, non-binary trigger, or short bursts only. It is also possible to restrict the firing mode by weapon categorization, for example "DMR" - semi only.
  •  Another limit is the maximum cadence of the weapon, i.e. the RPS limit. This limit is often forgotten.
  • And last, but one of the most important limits is the ammunition weight limit for a given field. The heavier the BBs, the higher its impact energy and therefore more dangerous. For smaller fields, it is therefore reasonable to limit the weight to medium weight - for example 0.30g, as it is played at relatively short distances. Whereas for large events in the woods, where fights take place at much greater distances, 0.40g or more can be used.
  • Other "limits" such as no shooting below a certain distance or only pistols in the building can be discussed another time. 

Measuring weapons, and how to actually measure them to get the most realistic data?


The standard measurement is with 0.20g and hop off. Unfortunately, this measurement is not at all indicative of the real performance of the gun.
With AS weapons the power varies with the weight used, so with some weapons with higher weight there may be an increase in power, i.e. the kinetic energy of the shot, the so-called "joule creep" (often depends on the propulsion of the weapon), with some on the contrary a decrease in power.
There is also a change in performance when the hop-up is set to different weight of BBs being used. For some weapons there may be a large drop in power of a few tenths of a joule, for other pieces the drop may be small, and for others there may be no drop at all. This also depends on the style of tuning of the gun and its propulsion.

So how to get the most realistic data when measuring the weapon limit? (valid for all weapon types)

  • First of all, it is ideal to measure the weapon directly with the ammunition that the player will use during the game. This eliminates any joule creep.
  • Another ideal measurement parameter is with the hop-up set for a given weight. This point is partially able to compare the differences between guns where the performance decreases or stays the same after the hop-up setting.
  • The last main parameter is to measure the muzzle kinetic energy (Joule), not the muzzle velocity.
  • Thanks to these points we can get ideal data to check if the player meets the limits of the field. Unfortunately, if something is ideal, it often clashes with reality.  
  • How many people will lie about the weight used?
  • How long does it take to switch the BB weight on the chrono or in the app?
  • How long does it take to check the hop settings when measuring?
  • So, won't it happen that because of the ideal measurement it will take much longer to check all players?
  • These points can therefore "break" the ideal measurement of weapons. Here it depends purely on the organizers of the event, i.e. how much time they have to measure, how much they make the measurement more efficient, or if they use compromises. Here I will try to list possible compromises of measurement.
  • Measurement of all weapons with the maximum allowed weight of the course, i.e. with the organizer's BBs.
  • Ignoring the hop setting, or just a check shot that the ball doesn't immediately fall down or fly into the sky.

And what is the main difference in AEG and HPA? 

Occasionally, some organizers have different rules for AEG and HPA guns, where HPA guns have a lower limit or more limited weight. Even among the players there is still a tradition that "HPA hurts more" or "it shoots much further".
So what is the "magic"? Well, nothing really - if we are comparing the same levels of weapons.  If we compare an HPA gun and a basic or slightly upgraded AEG, the HPA gun will shoot much better and farther. If we compare an HPA gun and a full-up (and properly) tuned AEG, both guns will shoot the same. For a bullet with weight X, muzzle velocity Y, and rotation Z, it doesn't matter what propulsion shot it. Also, in the equation for calculating the stretch kinetic energy, there is no variable for the gun's propulsion.

So even though there is no "magic" in it, we can still find a big difference when shooting HPA compared to most AEG guns. That is the compressed air propulsion instead of the piston movement. So the BB gains more velocity from the start compared to the AEG, where it hops through at a low speed (as the piston in the gearbox is still accelerating). Furthermore, a bullet driven by compressed air is hardly braked by the contact area of the rubber band (while in the AEG this braking also slows down the piston and thus reduces the bullet's velocity). For this reason, there is almost no drop in performance with the HPA once the hop is set for a given weight. So if you measure 2J with the hop off, it is very likely that you will still get 2J after the hop is set.

And now we're gonna get a little confused! 

So, is there a difference between them? Yes and no. As I wrote, if we compare the HPA to a basic or slightly upgraded AEG, there will be a difference, as there is no drop in performance with the HPA after the hop setting. However, if the AEG is well tuned (e.g. heavier piston, quality rubber with large contact area, soft pressure), there may also be no or only a slight drop in power after the hop-up setting. Then these guns can shoot the same. 


So thank you to everyone who read to the end. 


Author of the article - Racek Chief Service Technician - RacekCustomGuns
You can follow his work on Facebook and Instagram

Recently added

Up