Did ya read the barrel fitting info in the FAQs? You don't slide the feeler gauge blade in, you close the action on it, it should lock up tight on a .002" blade, .0015" should be very snug, .001" may slide out with some resistance, best to be tight. If the barrel is lose when locked up, it's too lose, it either needs shimming or the latch engagement isn't right.
There's no JohmDM in the member database, so I can't help ya there.
Tim