Sudden unexplainable low air pressure/fps

[Jaggardos]

I've got two guns, one a base G&P Spec Ops mostly SHS custom now M4 and an APS AKS74 with mostly SHS customs too.

Both were working absolutely fine on the last game day before last, no issues. Then comes the last games day and the M4 is getting sub 100 fps, even though I hadn't touched it at all in between the days. Opened it up to check airseal, piston -> cylinder is fine, cylinder head -> nozzle is fine. BBs flow through from the hop no issue. Whats going on? I dont understand how this can happen suddenly and I've spent several days trying to fix the issue and found nothing.

Secondly, the same thing has now happened to the APS. Tested everything, all fine, but still getting sub 100 fps.

Been using the same make of BBs throughout when they were working and when they weren't (BAW)

I've tried swapping out hop rubbers to no success.

Can anyone shed any light on the matter?

 

[Aengus]

Ever thought the problem might be with your chrono not the guns?

 

[Jay85]

Ever thought the problem might be with your chrono not the guns?

Click to shrink...

My first thought ?

 

[Jaggardos]

The bbs drop down after 5m at a really slow speed. I think the chronos fine. I understand how could think that though

 

[proffrink]

Torn bucking, cracked cylinder or just dry seals. How does it sound?

 

[Jaggardos]

Old bucking looked fine, tried brand new ones, cylinders are in tact and I've relubed all the o rings, as I said the gearbox is sound seal wise, nice amount of air coming out of it

 

[Sitting Duck]

Clean barrel, check m4 unit has tiny spring at hop unit pushing back to gearbox

thought hop must be torn (had that a couple of times) but you said you changed hop rubber

but that is a ton of air loss - like a girly silent fart coming out of air nozzle/front of box

not saying guru's walking on water can chrono by just putting their hand up in front of nozzle

but you get the idea that very little is coming out if box is barely farting out air

yup could be dry seals but still a friggin' lot of loss - many stock guns still produce 300

with not so great seals and poor cylinder head/nozzle sealing

depends if you wanna strip the box down and grease/polish cylinder, new o-ring, nozzle, ptfe tape etc....

(if not get a tech to look at it)

sounds like hop/bucking area and dirty as f*ck barrel, as first area to check out further

unless box is barely passing wind out of nozzle

another area is its been knocked out alignment box to hop causing nozzle to rub against hop and crap seal

but both guns go pear shape is a bit weird but not unusual....

says my my teching guru:

(soz it's a bit quiet lately and I'm stuck in with kids driving me nutz)

if it ain't hop/bucking/barrel area or defective nozzle failing to seal 101%

(could be snagging or weak tappet spring but this usually affects feeding)

it is gonna be a bugger/number of things to fully check out - might be a few things

but very likely it is gonna one stupid dumb a$$ thing - oooh yeahhh....

that must be really causing it to drop so much

M4 hop/barrel out pushed up against gearbox - blow down barrel and see if airtight

retract these slowly apart to see if it seals well or just barely seals when pushed home

soz I'm just trying to think of things to check coz not got it front of me

yup got some loss on some guns but nowhere that bad

 

[Jaggardos]

You're right, it is a stupidly low amount of air, thats why I'm clueless...

Theres a hefty amount of air coming out of the gearbox alone so I think thats fine

The new hop rubbers I got were G&G greens as I heard theyre pretty decent. On the AK they feed fine but on the m4 they cause blockages. When I put the original back in it feeds fine but with the low fps.

I'm pretty good with the tech side of airsoft guns, I know what to look for and have been able to fix most problems, but this has completely stumped me. I understand its most likely to do with the hop section, but unless I purchase a load of different barrels and rubbers until one combination works, I dont know what to do.

I've already greased and polished everything, as I said the gearbox is working flawlessly, its just the results that are poor

 

[Sitting Duck]

Try another hop unit, some of them can vary a smidge

Sometimes the lips can distort but this can cause poor feed or fps loss

Others can sit slightly further back and seal better against nozzle but again the nozzle may not clear enough to feed properly especially at auto speed

One thing to try is stick say an o-ring in front of hop, or piece of card to push back the hop unit to help bucking nozzle seal. But might restrict feeding if pushed to far back.

Tappet spring, could lop a coil off to increase tension to help seal firmly

Also loosen stock a bit as sometimes as stock is tightened tightly it can pull box back and front raises up that can knock the nozzle -hop out of alignment

Doubt if that was the problem but it might have got knocked out of whack

Trying to think of any things to check/try next