Beat Blaster gun course was a mission in Jak II. Krew rewarded Jak with the Blaster mod for his Morph Gun for which Jak had to go towards the gun course, where he also learned some wastelander moves from Sig as well as completing the training course to the Blaster.
For starters destroy the crate with the light beam pillar and pick up the new Blaster mod inside. Sig will then teach you some new moves over the communicator, afterwards you'll have to make a run through the gun course (similar to the Beat Scatter Gun course except this time you'll go the opposite direction). You need at least 4000 points before you can finish this mission.