The Soellkraft 8-Gauge Shell is used primarily in Weapon System Technologies' DTM Series Shotguns.
Background
This shell uses an extremely large gauge not used in the modern shotgun, the reason being 10 and 12 gauge shells are viewed as being powerful enough for almost all the uses of a shotgun. In the Halo Universe, the 8 gauge shell was reborn as the Soellkraft Hippo 8 gauge magnum round.
The gauge of eight is also equal to .835 inches, or 21.21 millimeters. The rounds use quadruple-ought, or 0000, buckshot. Oddly enough, twin zeros can be seen on the side of the shot shell boxes seen in Halo: Combat Evolved and Halo 2, suggesting that 00 buckshot is used. The box also indicates the rounds use 15 pellets in each shot, and counting the shot holes in a wall after firing will confirm this.
Quadruple-ought is .375" (9.5 mm) in diameter, and is immensely more damaging to a larger target than smaller shot sizes. The pellets themselves may be made of steel, or tungsten, and possibly lead or other metals. It could also be made from a mix of these materials. The title of 3.5" magnum means that the shell is that long. 3.5 inch magnum rounds traditionally contain the highest amount of powder of that particular size. Other smaller sizes include 3" and 2 3/4" rounds.
8 gauge shells are almost extinct as of today, but due to the shell's extremely high stopping power it is very effective, and it can kill a fully shielded Sangheili with one shell at point-blank range. The shells can also be used to dispatch several enemies at longer ranges. Each pellet is quite powerful, with only about one or two needed to kill an Unggoy in range and, needless to say, all fifteen pellets combined are devastating.
The reason that the 8-gauge shell is almost extinct in the real world is because it was considered a "destructive device" and subsequently banned in major countries, with the exception of a few who still use the gun for water fowling, but they were not very popular as 8-gauge black powder shotguns were far too large and clumsy to be used effectively (although they saw a large market in water fowling industries and boiler cleaning cannon slugs). Also firearms studies have found that the modern 12 and 10 gauge magnum shells are far more powerful opposed to an 8-gauge shell from one hundred years ago, due to better modern manufacturing techniques.
Trivia
- The hippo on the outside of the casing was included as a gift to Matt Soell, a former employee and Community manager of Bungie Studios with an obsession with hippos (Hippo in Halo) , and so the shell is named after him.
- The outline of a hippo can be seen on the outside of the casing by looking at a spent shell through the Sniper Rifle's scope, suggesting the name.
- In Bungie's recent update on the UNSC weapons, the shell dimensions for the M90 Shotgun are listed as 8 gauge 3.75", and may be a typo, but might also suggest the round used in the Halo 3 model use even larger magnum rounds than the normal 3.5" shells.