Sand blast gun

Had my HF blast cabinet for a few months. The gun is giving me fits . Clogs in a matter of seconds, maybe 5-10. Sand is dry ,screened. If I put my finger on the tip to blow air back wards it will unclog and blow sand again for about the same amount of time and stops again. Any suggestions for a fix or a different gun? I checked with Sears and TSC a couple days ago and they didn't have any. My old Sears hopper system works great with the same sand ,but then I have to do it outside and lose all my sand , not to mention peppering myself.
Yote
I had the same problem found my clear pickup tube becomes rough on the inside & sand tends to suck up in large segments rather than a steady pickup of aerated sand changed the pickup fixed the problem ,also dry sand no foreign lumps .