My MP40 is chrono'ing at about 200 fps
Can anyone offer any pointers why? And how I fix the feckin' thing... I am sooooo fed up of dodgy Chinese gun at the mo - my MP5k failed for the third time this weekend.
Turn the hop off, squirt some silicone oil down the barrel and clean it out with a pull through, then check the fps again. Try several shots, adjusting the hop very slightly for each one to see what difference it makes.
You sound unlucky, I`ve had five Chinese guns and none have failed on me 
Mine has a tendency to fire 2 bbs at once on semi sometimes, I would check it a few times on the chrono, if 2 bbs come out while chronoing it it will show low, just an idea, but the ACM mp40 does benefit from a strip down & re build, like I have said before its full of lithium grease indluding loads on the piston, it could be the grease has damaged the piston seal, lithium grease eats seals,
Steve.D
Mine also used to double fire - my local airsoft shop sorted that for me.
You've got nothing to ein, zwei, drei, vier
Thanks chaps - I'll try a thorough clean first then look at a strip down.
Can anyone tell a noob what this shimming and bushing thing is all about? I'm going to have to pause play due a new baby soon and plan to spend the time in between screaming and nappies getting to grips with gun technology!