265fps on a M100 Spring

[James Baker]

Hi Guys,

First post here but I have a search for similar questions with no avail but if I missed it I do apologise.

My brother in law just purchased a VFC 416 second hand and it's come with a M100 spring ( tested and confirmed in my masada getting 330fps). In his gun however it gets 260/270 fps, so I assume there is an air leak some where? The piston head/cylinder/ nozzle combo is air tight, not short stroked and no sorbo, it even has a bearing spring guide which should bump the fps up. I tried diffent hop rubber but still 270 fps. I'm reluctant to "solve" it by putting a bigger spring in and accepting the air leak. Am I missing something? Is there anything I can do about the stock nozzle/ stock hop unit interface? I would have thought that would have been OK being stock. But I can't think of what else the issue could be.

Any ideas welcome. Any hunches also welcome!

Thanks

 

[Iceni]

First question is are you absolutley sure what ammo you put in it, and what weight was it.

I'm going to treat you like an idiot for the minute and assume you know nothing. No offence but with one post you are an unknown.

If you have no idea about the ammo, or it came with the gun, then perhaps you are shooting 0.25g, 0.28g or 0.30g bb's and the gun is fine. It's just the chrono was set for the wrong ammo weight.

If you look at the chart, 330fps is 1.01 Joules of energy with a 0.2g bb. Equally with 0.28g bb's the same energy 1.01 Joules is 280fps.


I'm not saying this is correct, but it's a question that needs to be asked before you even open the gun and start to look for issues.

If you don't know about Joules, it's a unit that describes the energy of an object. With a bb more mass (g) means when you apply the same energy (J) the velocity (m/s fps) is going to be lower, but the energy in the bb is actually the same. Legally we measure energy output and not speed, hence why we always give the weight with the speed. 350fps on 0.2g ect.

 

[EDcase]

Hi and welcome James

Since you've checked the head/cylinder/nozzle seal the only other place I can think is the hop unit and rubber.  Just read your post again and read that you already changed the hop rubber so I guess its not there.

I'm not a gun-tech so I can't think of anything else.

 

[James Baker]

Thank you both for the replys,

Iceni, I'm new to the forum, but have been ti kering with guns for a while. Fully Aware the BBs I used for testing were blaster devil 0.2s. Which was the same ammo I used to validate the spring in masada. Thank you though appreciate the time and and handy chart to use for reference in the future.

EDcase, thank you for the warm welcome.

You may be on to something here! Regarding a frame spring! I can't see a spring on the hop unit ( other than for the nub). Should there be one over the barrel pushing the hop unit back on to the nozzle? If so I think you might have the answer! I haven't worked on  m4s before belive it or not!

Thank you!!

Edcase,

You are right! It's missing a spring pushing the hop unit back into the nozzle! Thank you so much.

Just got to find a spring now!

Finger crossed that fixes it!

Will update when  I have found a spring!

Thanks again!

 

[Iceni]

You may be on to something here! Regarding a frame spring! I can't see a spring on the hop unit ( other than for the nub). Should there be one over the barrel pushing the hop unit back on to the nozzle? If so I think you might have the answer! I haven't worked on  m4s before belive it or not!

Yup you'll need that part if it's missing. There are 2 styles an on barrel.

https://www.ak2m4.co.uk/internal-parts/hop-up-chambers/hopup-inner-barrel-tension-spring

 

And an over barrel that sits on a nub on the hop unit.

https://www.ak2m4.co.uk/internal-parts/hop-up-chambers/hop-up-chamber-tension-spring-small

There are pictures on both pages that show where they sit.

 

[EDcase]

Glad I might be of some help.

Iceni beat me to it ?

Usually there's a spring around the inner barrel or on the front of the hop unit (facing muzzle end) so that the hop unit gets some pressure backwards when the nozzle goes in.

Check YT for a disassembly video on his rifle to see which one it should be.

ak2m4 is on this forum and a great guy to get your bits from

 

[James Baker]

I think this is it! Looks like the bottom type of spring as there is a small knob for it to sit on! Than you again

 

[EDcase]

?

 

[Iceni]

Since you are ordering from AK2M4 I can highly recommend the zci rotary hop unit if you want an upgrade as well. It comes with all the parts including the spring.

https://www.ak2m4.co.uk/internal-parts/hop-up-chambers/zci-rotary-hopup-chamber-plastic-m4

 

[James Baker]

Thanks guys!  I have ordered the hop unit as suggested.  Will update you when I have it installed!

Thanks again

Also ak2m4... never heard of it before.  But looks amazing best airsoft shop I have found online!  Will used them again! 

 

[ak2m4]

Thanks guys!  I have ordered the hop unit as suggested.  Will update you when I have it installed!

Thanks again

Also ak2m4... never heard of it before.  But looks amazing best airsoft shop I have found online!  Will used them again! 

thanks bud, those inner barrel springs generally work great

 

[ak2m4]

Yup you'll need that part if it's missing. There are 2 styles an on barrel.

https://www.ak2m4.co.uk/internal-parts/hop-up-chambers/hopup-inner-barrel-tension-spring

 

And an over barrel that sits on a nub on the hop unit.

https://www.ak2m4.co.uk/internal-parts/hop-up-chambers/hop-up-chamber-tension-spring-small

There are pictures on both pages that show where they sit.

There was a small issue on those links, may have looked like the larger inner barrel spring was out of stock which it isn't

Small top spring
https://www.ak2m4.co.uk/hop-up-chamber-tension-spring-small

Large inner barrel spring
https://www.ak2m4.co.uk/hop-up-chamber-tension-spring-large

 

[EDcase]

The barrel spring is better than the top spring if you can fit one.

 

[ak2m4]

The barrel spring is better than the top spring if you can fit one.

I got in touch with @James Baker and included the larger spring.  James make sure you let us all know if that fixes the problem.

 

[James Baker]

So, update for you all...

First I tried the large spring on the standard hop unit - that wouldn't fit, I couldn't close the 2 receivers when fitted, to much material in the way even when fully compressed - option to cut spring down is still there.

Second the small spring on standard hop unit, this gave me 275 fps, remembering this is a m100 ZCI spring that gave 330fps in my Masada. 

Then replaced with the new zci rotary hop unit and included small spring...204 fps!? 

Also shout out to ak2m4, who managed to get those parts to me in record time! Thank you again!

Any ideas? am I doing it wrong?!

Kind Regards

 

[EDcase]

I've just tried an M100 spring in my new rifle. (A&K LR300) and also only get 260-270 fps.

I'm quite sure the piston and cylinder have no major leaks so I'm in pretty much the same situation as you.

I just ordered an M110 spring and new Maple Leaf Macaron (Thanks AK2M4 ?)  So we'll see what that does...

 

[Adolf Hamster]

side option if the spring doesn't fit- stack a bunch of o-rings up instead, has the side benefit of being a slightly tighter fit.

silicone hose also works quite well.

 

[James Baker]

That spring seems to be doing a good enough job at pushing the hop unit back, but the fps with the new unit took a bit hit, must be a hop unit/nozzle interface I think, not sure what to do about it though.

 

[EDcase]

Just to clarify, did you try the new hop unit from AK2M4 or adding the spring to the original one?

 

[James Baker]

Just to clarify, did you try the new hop unit from AK2M4 or adding the spring to the original one?

Both, the spring helped a small amount -270ish fps.

the new hop unit dropped fps to 220 ish ( done some tinkering since the 204 above but obviously still not great)