« on: March 06, 2013, 06:00:14 PM »
It's certainly a compression issue, and I hate to say it but you might have compounded the issue.
The "teeny washer" you're referring to: was it made of brass and about the diameter of the inner barrel? If so that's just a stabilizing ring, it has no effect on the actual air seal and simply takes some of the play out of the barrel when it's in the hop up. While you have the hop up unit out though its worth checking over the housing to make sure none of the parts are cracked or broken. I've seen a few AEG's through my shop with hop up units severed in half from various causes.
Filing the air nozzle probably wasn't the best idea, but you'll have to get the rifle firing again to see if it has any adverse effects on the function.
From the sound of it, it sounds like either the piston is cracked or the piston head is cracked/come off the piston. The first can happen regardless, most china pistons these days aren't bad but things do happen, a cracked piston could lead to inconsistent compression leading to the described range. The second, I haven't heard of a stock AEG doing it in a while, but again things can happen. If the piston head cracked or broke apart you will lose compression and again, leads to what's described, if the piston head simply came unscrewed and is flopping around loose as the rifle cycles it would also lead to the same results.
It's also possible the cylinder head has come apart. Usually clones use a polycarb cylinder head with a brass neck that the air nozzle rides on, these frequently come lose.
When you were filing the air nozzle was there any noticeable play in the nozzle? As in, extreme movement in any direction (forward/back, or side to side).
Since Echo 1 is a rebrand company, I believe the SA58 (SOF) series is a rebranded AGM (Quality Power) model. AGM has always been a bit low in quality control so really anything is possible. I would check the gearbox first as the symptoms make it clear something has gone amiss inside.