Has it been detail cleaned recently? Although Redhawk1 is probably right, I'd give it a thorough de-gunking and lubing first if not already done.
"The way you deal with Islamic State, these bloodthirsty, blood drunken terrorists, is to kill them, keep on killing them, until you kill the last one and then you kill his pet goat. That's how you deal with them."
Ltc. Ralph Peters