|4 Clip Design concept|
The other half of the evidence that I present in this image (above) is how the position of the clips that we see in the silhouette suggest that are 4 clips and not 3. The alignment of the clips makes much more sense in a 4 clip "X" pattern than a 3 clip concept. The front and back clips are in a darker orange with the two side clips in a lighter orange. Their tracks of motion are outlined in yellow circles and this kind of system could easily fit/work for the Hailfire's design.
I also have a sneaking suspicion that the Hailfire in the video is loaded with 6 round clips, since the design of each of those clips matches that of a normal 6-round clip. So my analysis reflects the size of 6-round clips installed in the blaster.