Where do you draw the line when it comes to spring power in metal gearbox blasters?
I’ve been gradually expanding my spring collection to have more tuning options, mostly sticking with the SHS M-series for consistency. While I have no intention of pushing any of our blasters past 340 FPS for the field we play on, I’m curious—at what point does it start to get risky for an off-the-shelf metal gearbox?
Does it start to get sketchy around an M120, or more like an M130?
I usually won’t go above an M100 regardless of metal or nylon box and don’t often use them anyway. My preferred spring of choice is usually M90 or M95, which gives me around 280 - 300FPS on a well setup rig. I’d expect about 320-330 from an M100, and around 350+ from an M110👍
Getting the airseal and compression 100% is the key… trying to up the FPS on a poor setup by overspringing it is just asking for gear damage or gearbox shell failure… not to mention battery drain.
How much spring is too much spring?
The classic Rok answer… it depends!
Most metal gearboxes will handle an m100 no problem for a long time. But the risk of breaking the front may be low but never none!
It really depends on the gearbox, and what work has been done if any and what parts are being used… and then you get a freak that breaks in stock form and the opposite where the bastard just won’t give up years later after 25rps 380fps abuse!
It’s worth noting I use tons of M100 springs, with good seals can generally get 330fps on a 330mm or less barrel with right volume and good seals.
380-400mm barrel good seals and volume you can see around 350-370fps.
An M100 with no short stroking is pretty safe upto 30rps if the barrel is 275mm or shorter, with an 80%port cylinder or less.
Full stroke sull cylinder I recommend around 25-27rps maximum.
Now I do use some M110 springs and a few M120… but they are usually short stroked which reduces fps, but decreases volume and the chance of premature engagement.
On M100 AND M110 you generally lose 15fps per tooth off.
M110s for me are for full stroke 380-400mm barrel power houses looking for around 380fps.
Or…
Blasters with short stroking 2-3 teeth but still wanting over 300fps with a gnarly 30 and up rps.
M120
4 teeth off, 35-38rps monster doing 350fps.
One of my cymas has run this for ages. I don’t use it much these days, as everyone on the field goes and plays elsewhere… and I don’t blame them.
Flex build territory lol
Now…
The other factors of making cast boxes last… in order of importance.
Volume.
Correct volumes help to create an air break effect as much as increase performance and consistency.
This is a must for both those categories.
AOE padding.
It actually means less than some techs make out for performance and reliability of the piston… more for shock absorption. It helps.
Choosing the right parts.
Yes alloy piston heads and cylinder heads may seem fancy. But if you have a cast box, trying to keep them in a good quality nylon version helps reduce shock. Example is on a wells, they have alloy cylinder heads, use a nylon piston head and aoe pad helps longevity loads.
A nylon cylinder head with an aoe pad, and a good flat nylon piston head reduces the weight of the impact and has more shock absorption, transfering less impact into the cast gearbox.
Radiusing.
Rounding the sharp corners of the cylinder cut out.
Spreads the impact energy across more area. It helps just use a small round file, remove as little material as possible and make the corners round instead of pointed.
A box with radius cast into it is best. Followed by a radiused box, then a box with no radiusing.
Best cast gearbox award: CYMA. End of.
I should make this a video with some examples!