Springs and FPS

Honestly, the majority of emails and messages I get about upgrading that start with “how big a spring should I put in first” is scary.

Power first. In the UK, our upper limit is 2.3 joules (j) of energy, which roughly equates to 500fps using 0.20g bb’s. The most common mistake for anyone beginning upgrades is to immediately think that they need to get this rifle to 500fps on a 0.20g and have it sitting right on the upper limit. There are two MAJOR problems with this. Firstly, chrono readings can vary from site to site so you need to leave yourself a little under to allow for that variation. Secondly, nobody sane will be using 0.20g bb’s on a sniper rifle. Generally we’ll be using weights heavier than 0.40g and thats where joule creep comes in. Without getting too scientific, a heavier bb carries more energy and will increase the energy of your gun at chrono. A heavier bb is travelling slower and will have more air behind the shot as it leaves the gun (from the air in the cylinder), whereas a lighter bb may well have already left the barrel by the time the piston is only halfway down the cylinder, with only have the air behind it. That’s where the extra energy is coming from.

Imagine you go to chrono at your site and for ease, most will put some 0.20g in your mag and you’ll fire at 499fps, with about 2.3j of energy, which is fine and the site let you go off to play. Now, you put 0.40g bb’s in and go and play. Because you’ve put the heavier weight in, your gun will now be firing around 2.7j. That’s absolutely not fine, and puts you over the legal limit. Now, I know some very well known snipers in the community will deliberately lie about bb weight, or chrono on a different weight, or turn the hop effect off to try and cheat the chrono. But that’s being a dick, and totally against the spirit of the game, and that’s not how we do things at Sniperworks. Always chrono on your intended weight and get it measured in joules.

As an example then, my rifle runs at around 465fps on 0.20, which may seem a bit low, but it’s 2.2j, which is close enough without risking going over on a dodgy chrono.

FPS isn’t solely dictated by the spring, because other factors such as airseal, hop rubber, barrel length etc will have an effect too, but it’s obviously a good place to start. On a good spring there’s usually an “M” followed by a number, which should indicate the strength in m/s. Unfortunately different manufacturers do seem to have a lot of variation, or different ways of measuring, or different numbers.

As a very rough guide to airsoft spring fps then…

  • M90 – 290-300fps
  • M100 – 330-350fps
  • M110 – 350-380fps
  • M120 – 380-410fps
  • M130 – 410-440fps
  • M140 – 440-470fps
  • M150 – 470-500fps
  • M160 – 500-550fps
  • M170 – 550-600fps
  • M190 – 650-700fps

Yeah it’s not easy, however there are two ways to adjust the fps and fine tune it. The most common one is to cut coils off the spring to make it shorter, to reduce the fps. So you can go a bit higher, and carefully remove a coil at a time to bring it down a bit. The other way to do it is to add spacers like these from Rapax. These slide onto the spring guide and reduce the space available for the spring, so increasing fps. Bear in mind that a more powerful spring is going to be stiffer and much tougher to pull back. This may be a factor in your style of play. A good quality spring, like Rapax or Laylax will be more consistent, and offer a lighter pull for the same or higher fps. The Rapax springs only come in a 2j or 3j, which makes spring selection a lot easier. Laylax has been at the top end of rifle upgrading for a lot of years now. The only other brand I’ve used down the years for springs is Action Army, who I haven’t had an issue with. It’s not a particularly technical part to go into too much detail.

Most stock rifles now will be around 420-470fps from the factory anyway, so if you’re on a budget, there’s probably no urgent need to upgrade straight away in order to get out and get playing.

And that’s pretty much all there is to the springs section. Stay under the JOULE limits (not FPS on 0.20) set out by your local laws and don’t try and cheat chrono. There’s very little to gain, if anything, but everything to lose.

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