I think you should be able to push it by hand. I'm not sure if your gun has a replaceable liner but you could try blowing air through it. Being sub-arc I would guess it gets used a lot. If the drive rolls are a little tight (or lots of use) tiny bits of wire will flake off and can plug up the liner. Dry graphite spray in the liner could help too. A lot of flux-core wire has a graphite coating. That's why your hands get black when you handle it. Check the contact tip too and make sure there are no sharp bends in the gun cable.