Best spring to achieve 500fps with a 0.2g bb?

[Tommygunn]

I have a CA M24, with PDI cylinder and piston, which is fitted with a First Factory 170 spring which used to give me a near spot-on velocity of 500fps with a 0.2g bb. However, the spring is getting on for nine years old and is losing fps.

 

What are the other options out there that people have tested, in lieu of another FF 170 spring?

 

Cheers,

Tom.

[Lightbulb]

Have you tested for air leaks at the cylinder head and the barrel? You might get away with a 150.

 

170 and cut it is a common way. Depends on the barrel length though.

 

I use a 150 in my gspec (get around 450). But someone on here just fitted a longer barrel and gained 50fps.

 

---

 

Or do you just mean what other brands?

[Tommygunn]

I think you may have misunderstood my post. My FF 170 spring has always been good on delivering 500fps but it seems to be tiring and I've lost about 30fps + or - and I'm near 100% sure the cylinder head and nozzle/hop unit are tight.

 

I'm pretty sure the spring is just tired so, yes, I'm just looking out for alternative brands that people have tried that can put out an equivalent power.

 

Tom.

[Lajjvo]

Is a FF 170 spring rated in a similar way as the guarder m1** system? In that case, you have a mayor airleak as you should be getting 170 m/s (~560fps) and not 152 m/s (500fps)

 

On the matter. Any m150 or similar rated spring should get you to 500 fps and beyond in a airtight system.

[Tommygunn]

Lajjvo,

I have no idea how different manufacturers springs compare to one another, does anyone?

 

I've just done a complete strip, since I began using it again, and in this time it has seen about four Sundays of heavy use.

Anyway, first test was how air tight it was. The cylinder is absolutely fine with no leaks, however, I have discovered that there is a leak between the hop unit and nozzle.

What I did was mate the inner barrel/hop unit to the complete cylinder and I blew down the barrel only to hear a whistling. The air was exiting past the small 6mm o-ring that seals around the nozzle just before the hop rubber.

I removed it and it turns out that the o-ring has lost some of its zest and is definitely not a friction fit with the nozzle, there is in fact daylight between the two.

 

The FF170 spring was fitted back in 2003 and after the strip I found a 25mm, pre-tension spacer in the piston, which I'd forgotten about, plus about 3mm worth of washers on the spring guide, which I knew about.

 

So, I need to replace the 6 x 8 x 1mm o-ring.

 

Now, though, I want to get rid of the 25mm spacer and fit a stronger spring. Has anyone used an FF 190 spring and what velocity did you achieve?

 

Tom.

[Lightbulb]

In theory it is as stated above. M150 gives 500 fps. It might vary a bit (i would guess 5 to 10 fps for 'decent' manufacturers).

 

Considering that a normal length vsr with get about 500 with a m150.

 

My gspec gets 450 with 0.2, but as I said this is due to the short barrel. People say this is because the bb is out of the barrel before all of the air from the cylinder which make sense to me. If I use a heavier bb it will be in the barrel longer, as heavier means slower, but it will gain more energy. As you may know energy is the important thing. A car hitting you and 10mph will hurt a whole lot more than a bb! Anyway, I measured the fps then calculated the energy for a 0.4 bb then worked out what it would be if it was a 0.2 and it came to about 500.)

 

So very long post to say: if you fix your air leaks a m150 might be enough, a m170 definitely should be. If you have a short barrel you might be getting more energy with a heavier bb so it might not actually be such as issue.

 

A 190 will be hard to cock, and will wear the internals quicker.

 

I'd go with another 170 if I were you. Why do you not want another First Factory m170?

[Tommygunn]

The inner barrel I'm using is a 509mm KM 6.04mm.

Currently, I'm soaking the 6mm o-ring in silicone oil to see if I can expand it a bit to eliminate any gaps.

 

I'd go with another 170 if I were you. Why do you not want another First Factory m170?

 

I didn't say I wanted to buy a new 170 spring. I'm interested in a 190 spring as long as it allows me to maintain 500fps/0.2g and get rid of the spacers. Ideally, and I'm going to be doing some more testing when everything is ready, I'll see what my 170 spring is doing without the 25mm spacer.

Either I'll end up keeping the 170 and the spacer or consider going over to a 190 spring.

 

Tom.

[Lightbulb]

Having read what you have said again I have a question: Why do you want to use a stronger spring instead of the washers? Will it not just be harder to cock?

 

Or do you mean to take a 190 spring and cut it down to give 500 (since as we have said a 190 spring should give like 600fps in a well sealed system)?

 

Some people say that higher rated springs cut down will not 'weaken' as much. This could be true as if they are shorter they will be under less compression when the rifle is not cocked (although in my experience higher rated springs are longer to start with).

 

However best thing to do if you are storing a rifle for a long time without using it is to decompress the spring. No compression, no weakening.

 

(By the way sorry if you know this but its helpful for others I think).

[Tommygunn]

Right, I've done some fixing, repairs and maintenance.

 

There were a few issues when I initially stripped the rifle.

1. The cylinder head had actually partially unscrewed itself and I don't know how long it had been like that.

2. The spring guide had partially unscrewed itself from its base.

 

I have now reconditioned the 6mm o-ring (actually ongoing and currently soaking in more oil), I have removed the 25mm spacer and one of the washers on the spring guide.

 

I am now getting an average of 493.1fps with ten shots.

 

What I will do is remove the last spring guide washer and add a 9x17x5mm thrust washer, just ordered, which will make it easier on the spring and slightly up the fps to a near perfect 500fps.

 

I would say, that it seems, it all comes down to air leaks and I will be sticking with my First Factory 170 spring.

 

Tom.

[Lightbulb]

Hehe.

 

So after all that the first sentence I wrote was correct.

 

Cheers for letting us know. Always nice to know how these things turn out.

 

You could put some lock tight on spring guide to stop it happening again. I might leave the 7fps just in case a site chrono reads it higher. Sites where I play 501 = no game.

[Tommygunn]

Just to tidy this post up, I received the thrust bearing but it was just a fraction too tall so preventing the piston from retracting all the way and engaging the sear. Yes, I gave the spring guide a liberal dose of threadlock.

All is good.

 

Tom.