265fps on a M100 Spring

[James Baker]

50 minutes ago, Lozart said:

 

It's entirely possible that your two points of comparison are leading you astray. Your Masada might well just have a particularly good seal, I have an M4 running an M85 spring that hits 325 fps quite happily.

 

306 does seem low but it may just be the best that gun can manage with the specific combination of parts you have. When you say the cylinder/piston/nozzle is airtight, how did you test it? Is the cylinder right for the barrel length?

Thanks you for your reply,

Yea I know its not apples with apples, I was just wondering if I should be trying to "fix" the air seal more before putting a bigger spring in. 

Barrel length and cylinder are stock - can't remember where the port is on the cylinder or even if it has one- will check next time I go in.

I tested it by putting putting the nozzle on the cylinder head and ramming the piston down there with my finger over the Nozzle.

I did just try it with my Masada barrel (6.05 PDI) but unfortunate the gun wont feed with that setup. the hop rubber block the bb from entering. so can't rule out that making a difference.

 

Sorry should have said stock barrel length is 275mm

[EDcase]

I think 306fps from an M100 is acceptable.

There won't be one single thing you can change to improve it.

Edited March 24, 2021 by EDcase

[ak2m4]

@James Baker I've got some old spare Rocket M115, you're welcome to grab one for free.  It should put slightly over 350fps but then you can just a coil.  Message me 🙂

[James Baker]

3 hours ago, ak2m4 said:

@James Baker I've got some old spare Rocket M115, you're welcome to grab one for free.  It should put slightly over 350fps but then you can just a coil.  Message me 🙂

That's very kind of you. I have a few spare springs....and have now solved the problem!

 

I put a bigger spring in the gun, that got 370 in my masada, still got 300 in the 416....so as it turns out...

 

The issue was the ported cylinder! The stock cylinder has a port at 4/5s ( my guess). I didn't consider that to be the limit with a 275mm inner barrel...and I was wrong! Just put a full cylinder in there. 360fps now! What a roller coaster!

[James Baker]

Update: I wanted to check the m100 spring in the full cylinder...Still only gets 300fps, and that was only after rebuilding the hop unit as initially I was getting 160ish! 

There is still something I don't understand! A spring that gets 370 in the masada gets 360 in the 416.

The M100 gets 330 in the masada but only 300 in the 416. I think there is a random factor such as nozzle to hop seal which changes slightly everytime I open the gun up! It's very confusing!

[EDcase]

Yeah its a rough science.

 

The only thing I can think of besides randomness with fitting is maybe the O-ring seal around the piston head.  With stronger spring=higher pressure maybe it expands more to give a better seal...?

[James Baker]

52 minutes ago, EDcase said:

Yeah its a rough science.

 

The only thing I can think of besides randomness with fitting is maybe the O-ring seal around the piston head.  With stronger spring=higher pressure maybe it expands more to give a better seal...?

Solid logic, that said my rudimentary test suggests it's got amazing air seal even at very low speeds. Will put the bigger spring back in tomorrow,  minus a coil and see how that does!

[Adolf Hamster]

Thought popped into my head- whats the state of thrust bearings in the 2 guns your using?

 

That'll change your fps a bit depending on wether you're running one, both, or none.

[James Baker]

32 minutes ago, Adolf Hamster said:

Thought popped into my head- whats the state of thrust bearings in the 2 guns your using?

 

That'll change your fps a bit depending on wether you're running one, both, or none.

Thrust bearings being on the spring guide and piston?

Masada has no bearings, just a washer/shim on spring guide.

416 has a bearing on the spring guide, so theoretically, in my head the 416 should have higher fps if all else were equal.

 

While I think about more trial and error tomorrow, is there a down side to having a non ported cylinder? I get it will mean it throws more air out the end if the barrel, does this actually have any negative effects, I have read accuracy can suffer, but haven't had this issue on my masada with a full cylinder. 

[Adolf Hamster]

13 minutes ago, James Baker said:

Thrust bearings being on the spring guide and piston?

Masada has no bearings, just a washer/shim on spring guide.

416 has a bearing on the spring guide, so theoretically, in my head the 416 should have higher fps if all else were equal.

 

While I think about more trial and error tomorrow, is there a down side to having a non ported cylinder? I get it will mean it throws more air out the end if the barrel, does this actually have any negative effects, I have read accuracy can suffer, but haven't had this issue on my masada with a full cylinder. 

 

hmm, so not the thrust bearings then. generally i like to run at least one on the guide but skip the one in the piston to save weight.

 

in terms of ported/unported cylinders, aeg's have a bit of flexibility (hpa's for example tend to be much more sensitive to volume where it really does matter, but then you can also adjust it much easier). i have run unported cylinders on shorter barreled builds in the past and it's worked fine.

 

better to be over than under, and ultimately if the gun shoots good it shoots good, doesn't matter how you acheive it.

 

by all rights it *shouldnt* make a difference if the existing volume is correct, but evidently there's something weird going on here.

[Ad_]

I always try to optimise air seal and compression for best efficiency and minimised wear, and in my experience Guarder SP90 springs are good for ~330-340fps with the right selection of parts (as has been the case with my P90s, MP5, M933, HK416, AKS74U).

 

To achieve this I typically use the Guarder chromed cylinders, the pistons are either stock or polycarbonate pistons with Lees Precision aluminium piston heads (but with slightly smaller O-rings), air seal nozzles (the nozzle should be just long enough to press the feed lips on the hop rubber against the hop chamber & form a seal), Prometheus purple or Maple Leaf hop rubbers and 6.03mm tight bore barrels. And always using a bearing spring guide, never with a bearing piston head.

 

Piston O-rings can make a big difference; you want a good air seal but you don't want a tight fit as the increased friction from a tight fit will reduce performance. I always try to find O-rings that fit the cylinder as loosely as possible while still providing an air seal; the best piston O-rings I have actually barely seal at all if you cover the nozzle with a finger & manually push the piston, but when the piston is moving at speed the pressure ahead of the piston / airflow through the ports in the piston head expand them out to seal perfectly. I measured the better O-rings & found them to have an outer diameter of about 23.7mm while the LPE piston head O-rings are 24mm.

 

Another thing I've done with a couple of them is to slightly increase the piston weight (only by ~2-5g though), which I did after installing a polycarbonate piston that was much lighter than the stock piston and noticing a reduction in power afterwards. Be *extremely* careful if doing this though, as it'll slow the piston down and slowing the piston too much will result in catastrophic failure. Also this probably won't help on unported cylinders (the intention with this is to increase the energy in the piston and immediate compression once the piston accelerates past the port in the cylinder & compression begins).

 

Your choice of cylinder lubricant can also make a big difference; I currently favour TechT Gun Sav but Super Lube silicone grease (which you can get from AK2M4) is very good too. Be careful not to apply too much though, it only needs a fine coating...

 

There are a lot of factors though and tolerances in Airsoft can vary wildly so none of this can be guaranteed for any particular gun.

[James Baker]

Thanks Adolf and  Ad,

 

Some good points to look in to tomorrow.

 

Something else I have just thought of, there is a sector delay chip in there, which I can't belive is needed, so will try removing that tomorrow as I could be keeping the nozzle from making a good seal at the right time....maybe.

 

Lots to dream about and try tomorrow! Thanks all

 

[James Baker]

Another update, took it all apart at lunch to remove the delay chip, after that test firing 20 ish bbs the first shot was 330 then all 300, first time I have seen 330 on this spring. 

Now convinced that the gear box can do 330, i concluded it must be a nozzle/hop interface, so rebuilt that ZCi unit again. test got about 2 shots in 20 at 320/335.

So tried the oem Hop unit. now consistently firing at 325/330. Which is a shame as the ZCi hop unit seemed to be a more capable unit in terms of Hop, but rubbish in terms of air seal (in this specific gun). Any ideas how I can make it better?

 

Kind regards

James

[Ad_]

I remember hearing somewhere that VFC guns can be a bit fussy about hop units... you could try to find a nozzle that works better with the ZCI chamber, but my recommendation would be to just keep using the stock hop unit. AFAIK the stock rotary hop units that VFC use are decent enough anyway, just be sure to use a good hop rubber & nub.

[James Baker]

Yes it would seem your right!  So I have put the stock unit in, with a maple leaf rubber and a new nub. Now shooting at 330 consistent. So leaving it there.

 

I did sand back the ZCI hop unit to get it closed to the nozzle which did increase the fps to 320 ish from 300. But couldn't take any more material without interfering with the dial.

 

So stock unit with  a cut down ( alot) large barrel spring with new rubbers, sector chip removed  seems to have it sorted. Thanks for your help all! 👍