very weird problem: 3 mechboxes with 100 fps loss

[Jimski]

ok thank you guys, this is helping me a lot.
keep it coming!

[Jimski]

Originally Posted by ancorp

I had a 250fps drop (150 instead of 400) on an AK before, because the ICS gearbox shell was ever so slightly misaligned with the hopup unit. Replaced it with a Cyma shell and it was good to go... don't know if that helps, but big FPS drops can be had, much more then 130fps.

interesting, I wonder if the sloppy AUG system can bring such problems.probably

Originally Posted by BORDENSNIPER

broken nozzle/craked nozzle

dead oring on piston head/cylinder head.

hopup rubber is chewed up/torn

too much grease/oil

dirty barrel

retard spring.

any combination of these WILL result in fps drop.

ok I will check the grease factor also, I wonder if they are spewing grease.

[Sha Do]

With the grease thing, make sure that there is just enough to slightly coat the gears and the inside of the cylinder. Barely any is required in the piston and tappet plate slide areas. Most stock guns come with way too much grease on the gears, but too much grease would not result in that much of an fps drop.

With the mech box alignment, this usually does not affect an AUG. It can make a huge difference in an AR, but the AUG mech box either fits or it doesn't (unless the plastic insert plate is loose). Check to make sure that your inner barrel is not sticking (should move freely). Also, make sure that the outter barrel has no play (in and out) from the AUG receiver, and make sure that the upper and lower receiver have no play. Any excessive play in either of these places will cause air loss at the hop up, and could also result in the mis fire you described.

SHA DO

[Danke]

Go here for AUG info. You'll need to sign up but it's worth it.

http://www.arniesairsoft.co.uk/forum...64&hl=helpdesk

Seems like you can have the mechbox break loose and start to migrate backwards compromising the seal and dropping the velocity. Fixes for both the minor and the major types of this failure are listed in the thread.

[SHÖCK]

Did you do a compression test on your cylinders? Hold you finger over your nozzle (nozzle installed, maybe even tappet plate as well) and push the piston with your other hand like a syringe and see if air leaks.

Put it into a tub of water and see where the bubbles come from.

[DarkAgent]

U said they are ok mechanically but id check the bushings.

My old CA G36C had a deformed bushing once that brought the fps down to like 95ish.

that was running stock so check that if you haven't already.

[Jimski]

thank you guys!
I did compression tests but I will redo them when taking the mechboxes apart.

I don't think it's anything mechanical since it's been checked recently, I'd go for the sealing problem.
Although it could actually be something mechanically slowing down pistons.
I'm waiting for some parts, and I'll post comments asap when I get new results.

[DarkAgent]

well its not something most mechanics would notice right away.

I was at Ashbash when it was in California and the airsoft extreme tech didnt notice it but the redwolf tech did.

[Kos-Mos]

Check your actual hop-up body.

I had to change one in my friend's AUG because there was a little, barely visible crack in a corner where the barrel clip goes.

Changed for a metal one (and had to modify it to fit properly, better with a stock one).

voila!

If you have spare time this week-end, you can drop to my place. My AUG is currently shooting 398fps on every shot. With that, we can surely find where is the trouble.

[smurata1]

Good thing the AUG is easy to disassemble.
Have you tried another known good hop up packing? Did you try a known good nozzle; some aftermarket nozzles have little o-ring(s) on the inside diameter to help seal too.

I had a problem with a Marui G3 that I was scratching my head on for a while. It was set up with Guarder FTK and a PDI 170. Clocked it with the Guarder Speeder 2000 at just over 290 fps w/ 0.20g bb= WTF? Went with an Action o-ring nozzle and Guarder Clear Hop Up Packing and got 345 fps with 0.25g. I had to clock it with 0.25g bbs because I had run out of 0.20g.

Anyways, my two cents on the bit. Didn't think that those 2 components made that much of a difference.

[Jimski]

thanks a lot Kosmos and Smurata1, I think your suggestions are close to my problem's solution, but I can't really be sure exactly how:

Sooo tonight I added a metal hop up.
the metal ring can't really fit between the hop up and the barrel; how critical is it exactly ? I stuffed it as deep as I could...
other than that, at the barrel level the seal seems ok...when I blow into it

I also changed the cylinder set for a systema one on the first mechbox.
The cylinder head is suprisingly loose in the cylinder.it is ventilated.
The spring is not reverted (linear end front,compressed nonlinear end towards shooter)
aaand I added a metal nozzle with the O-ring.

it still shoots 249 fps!


I checked the seal with the bucking when the barrel is mounted, it looks uber-perfect.
Could there be a leak at the junction mechbox-hop-up ?

[Jimski]

soo here is where I am now:

it is either:
-the piston being too slow ( bad spring, bad slide)
-air leaking from the mechbox/hopup junction (mechbox and body related), from the nozzle/bucking junction (assembly related), from the hopup/barrel junction (hop up body related) , or from the piston O-ring (brand new and bought as a set with the cylinder).

I just changed the O-ring on the piston head, compression is gold, ventilation to avoid suckback works.
I am wondering about cylinder porting and barrel length now.
fps test tonight.
cheerz

[Jimski]

ah ah
tested mechbox 1 with short barrel, got 131 fps at first shot and around 240 afterwards (should be around 340 lol )
after that something went krrr krrr krr so I have to check it out again.

so far each testing has brought me even less fps than before

tonight I'm testing mechbox 2 (should be around 380 fps) with both barrels.

next game I'll probably just bring my inner barrels and blow BBs with my mouth, sarbacane-style.

seriously I have no idea what is wrong, everything is perfect.

[Styrak]

You should send your AUG to me and I'll fixy fixy.

[dontask]

Originally Posted by Jimski

ah ah
tested mechbox 1 with short barrel, got 131 fps at first shot and around 240 afterwards (should be around 340 lol )
after that something went krrr krrr krr so I have to check it out again.

so far each testing has brought me even less fps than before

tonight I'm testing mechbox 2 (should be around 380 fps) with both barrels.

next game I'll probably just bring my inner barrels and blow BBs with my mouth, sarbacane-style.

seriously I have no idea what is wrong, everything is perfect.

Oh I had the exact same problem that you're having. You should check your shimming because what's happening is that the gears are too loose inside the mechbox and when you pull the trigger the gears will give way and spin in reverse letting the piston shoot forward before it is pulled back all the way (hence the low fps).
Check if that works for you.