Sometimes it could be something as simple as the type of shell you are firing, I believe when discharged a federal 3.5 will be a little bit longer than others... sometimes that fraction of an inch will be enough to "catch", try a couple of different rounds and compare. If that isn't the problem, then I'd look towards the gas or recoil system... sometimes people use a heavier gun oil and that can impede the cycling action, with autoloaders I've found that less is more in terms of performance...
I hope that the above listed suggestions are your problem and not a problem with the gun itself. Hope I've helped..
DD out