black fox's tricks of the trade

[Mongrol]

I just went over the sticky and am applying it to one of my guns. Im almost done but stuck with what spring to put in to shoot 400. I have a systema type 3 cylinder with a good seal. I read that you can achieve max distance and velocity with a weaker spring if the parts are properly installed. Can someone explain this to me? I i have a ported cylinder how is it that a weaker spring can achieve higher velocity than a stronger spring. That said, can someone recommend a spring that i can use to achieve 400 fps with a type three cylinder? Its an E1 mp5 (older version i believe) and the spring it came with was shooting 400 with (type two cylinder?) i think thats what it was at least.

Thanks

[Cap n pickles]

Get a M115.

If you have a TBB of 6.03 i would say a M115 or M110. Maybe a M113. Springs are pretty cheap if you look at the right places.

[Mongrol]

that should put me at about 400? From what iv read it makes sense but i dont understand the logic behind it.

[Falcon7]

Ported cylinders are for shorter barrels like yours because they don't need as much air to fill up entirely. A stronger spring = faster air = faster bb. For a gun with a long barrel, upgrading to a non-ported cylinder can up the FPS without using a stronger spring. Why do you want a 400fps smg? Consider a barrel extension inside a silencer if you are using it for outdoor games.

[Mongrol]

Cause I have a kwa cqb for indoor thats all set up. If used the mp5 I would have to buy rails for my stuff and I dint really want to do that

[league 4]

that should put me at about 400? From what iv read it makes sense but i dont understand the logic behind it.

An SP110 spring can get you 400FPS. It gave me 399 with .2's with decent compression and a tightbore.

[Mongrol]

mkay thanks

[Black Fox]

Jaydork

The purpose of matching your barrel length with the proper cylinder is all about maximizing energy efficiency.

As Captain Pickles said, with the ported type-3 cylinder and using an M-115 spring, you should get close to 400 fps (depending on the tight bore barrel you are using and upgraded internals).

For the sake of argument let's say the M-115 with the type-3 cylinder gives you 400 fps on your MP5. Now let's you changed the cylinder to a type-0 (full with no ports). Most likely the velocity will drop to around 385~390 fps. Now let's say you want to keep the Type-0 cylinder. But if you want it to shoot 400 fps you will need to change it to an M-123 spring.

MP5 barrel+Type-3 cylinder + M115 spring = 400 fps
or
MP5 barrel+Type-0 cylinder + M123 spring = 400 fps

Because the Type-0 cylinder does not provide maximum energy efficiency, you have to use a stronger spring to achieve your 400 fps. This means your gun is working harder. Thus, needing more juice to to turn the gears and creating more ware & tear on the gearbox because of the harder impact of the piston from the stronger spring. (See further explanation in red and blue below)

I also noticed that when you have the proper cylinder match to the barrel length that you are using that you generally have a much tighter BB grouping along with better range. I can't explain the science as to why, but I think it has to do with the air pressure around the BB just as it leaves the barrel.


However, one example that I do remember the details on was a friends Tokyo Marui AK Spetsnaz that I was working on. I had an M-130 spring and a stock barrel (229 mm). When I put a full Systema Type-0 cylinder in it shot around 370 fps. When I put a Type-3 cylinder in it, it shot nearly 400fps. That was almost a 30 fps gain! (With an Excel 0.20g Bio-BB). Now when I asked my friend who worked at Systema about this. His explanation was that if you looked at the Type-3 cylinder. The forward end of the port is almost in the middle of the cylinder. This mean the first half of the piston stroke had very little resistance since the air was bleeding out through the holes. Because of the low resistance, the piston was able to gain more speed and therefore was able to impact the remaining air after the ports at higher velocity which translated to higher fps. He said when a piston travels through a full cylinder, the speed is not the same through the whole stroke. As the piston move closer to the cylinder head it picks-up speed and reaches it's maximum speed just before it completes it's stroke. So when using a full cylinder on a short barrel like the Spetsnaz. The BB has departed the barrel when the piston is only half way through it's stroke. And since the piston has not yet reached full speed. The BB is not receiving the full amount of energy that the spring is capable of providing.



"Mini-Marine"]OK I think I see what you're getting at.

What you are saying is that with the proper cylinder is more efficient and will grant higher FPS with a given spring, therefore you can achieve cap FPS with a lower power spring, which will in turn result in less wear and tear on the internals.