Air pockets in tails does not always mean air in the injector. I get them when I don't fully push on the injector at the end. Depending on the mold most fill from the lowest point up. But if there is a narrowing near the tail it will require q final push at the end to force out any air left in the tail. On the comment of heating your plastic to 350, I never do this and never have a problem. Mine get to 330-335 and never any hotter. Getting it that hot put you real close to the point of no return( yellow plastic). You need to really know your temps if you get it that hot but in my opinion is not nessesary. These comments come from shooting about 5-6 drums a year by hand and no magic machines. If you get an infrared temp guage make sure and stir while you are getting g a reading, strait from the microwave it will have hot spots. Good luck.