While you're at it, I'd also triple check that the gas key isn't slightly loose - it might be tacked down vertically, but if it has some yaw play in it, those can bind on stuff (and have the severity affected by what CH is in use). May not be the exact issue in question, but an odd one I've experienced that manifested similarly (but not in the same way).
عندما تصبح الأسلحة محظورة, قد يملكون حظرون عندهم فقط
کله چی سلاح منع شوی دی، یوازي غلوونکۍ یی به درلود
Semper Fi
"Being able to do the basics, on demand, takes practice. " - Sinister
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