I dunno, 15 seconds isn't very much... why not just give it to the engineer and make it smaller

This category is most popularly represented by the E-Web, which was seen in the Echo Base hangar as a group of "snowtroopers" attempted to set it up prior to attacking the Millenium Falcon. Some of the apocryphal literature describes extremely long setup times (anywhere from 5 minutes to 15 minutes) for this weapon, but those setup times seem ridiculously exaggerated in light of the fact that the snowtroopers were trying to set it up and use it on the Falcon before it could escape. Real-life GPMGs are designed for maximum ease of use and setup (a competent crew can set one up in less than 2 minutes), and there is no conceivable reason that the designers of the E-Web would have thought any differently. You can see evidence of the E-Web's true setup time if you simply watch this scene carefully: just before Han Solo fires a burst from the Falcon's drop-down automatic weapon (roughly analogous to the .50 calibre machine gun commonly mounted on modern infantry combat vehicle), it looks like one of the snowtroopers is already getting ready to fire the weapon! The reason for the grossly exaggerated setup time is probably due to the well-established New Republic bias in the official literature.

In any case, the E-Web is analogous to a very heavy machine gun, even larger than the wide-barreled automatic weapon the Rebels used in their futile defense effort. It expends power at such a prodigious rate that it requires a dedicated crate-sized power generator (see picture at right), which is an ominous sign considering how destructive their relatively tiny handguns and blaster rifles already are. Any group of infantry caught in open ground through the sights of this weapon would surely be blown to steaming bits in seconds, and the weapon seems to have light armour-piercing capability as well, since the snowtroopers intended to penetrate the Falcon's hull with it. A weapon like this can dominate a battlefield if properly positioned, as demonstrated in real life by the carnage German machine gun emplacements inflicted on British, Canadian and American forces as they pushed ashore on D-Day.

You may notice the large sighting attachments on both the Rebel HMG and the Imperial HMG. Both of them appear to incorporate some sort of powered scope, but unfortunately, the films never showed us the view through either device, so we have no way of knowing what sort of information is being conveyed. At an absolute minimum, I would expect that the information is equal to what a pair of electrobinoculars would provide. Since these weapons are apparently capable of multi-kilometre ranges (given the ranges at which they were used in the Battle of Hoth), the scopes make sense, and I would presume that there is some sort of internal scope adjustment mechanism.

Of course, very large HMGs like the dreaded E-Web are not the only machine guns in the Empire. The Blastech T-21 (seen in the hands of the foreground stormtrooper in the picture at the top of this page) is described by the SWEGWT as a "common support weapon for army and stormtrooper squads", precisely as expected for a GPMG. Its power pack (ie- ammo clip) only has 25 shots, but the gun can also be hooked up to a 20 kg backpack generator (analogous to a box of belt-feed ammunition for a machine gun) that can feed it "potentially unlimited fire capability". The weapon has light anti-armour capability, and is said to be capable of blasting through armour suits, force fields and even the hull plating of armoured landspeeders.