Have you downgraded the spring? even on the g36 you had?
The spring in those are really high for importation reasons, and shooting repetitively with one of those will/could destroy your piston and gears.....
PS: I used to be a SRC hk416 owner myself, and to be honest, I think they are great..... but looks like some ppl get awesome guns, and some othes get Lemons.... LOL
PPS: have you bought it from Ken @007airsoft? he could help you with this problem himself....
"A workout isn't easy, but neither is being fat, make the right choice"