Designated marksman (DM) is the classification that fills the gap between snipers and assault class. DMs use weaponry that can reach a higher effective range than most assault class people but a lower effective range than most snipers. The rifles that DMs use are called DMR's (designated marksman rifle). This class can often exchange names freely between many other names such as sharpshooter, military marksmen, squad marksmen, ect.
DMRs are almost always electric, however, they can be gas if built correctly, and rarely can be spring. DMRs are very often based off the M4 platform. The most common DMR is the SR25. This gun is very similar to the M4 platform but the internals differ to accomplish higher ranges. The key difference is in the cylinder. The main factor that gives any gun range as stated in the info page 0000, is cylinder volume. The SR25 has a longer cylinder which also means it has a longer piston and different gears. This can make the gun shoot slower rounds per second than assault rifles but that is never the point of DMRs anyways. Often times, in order to be considered a DMR, the gun must be semi locked (only capable of shooting in semi auto), or, only have the options of safety, semi auto, three round burst.
There are a few other versions of DMRs but they do not achieve the same cylinder volume as the SR25. other options include long-barreled M4s or M16s, SL9, L85, and M14.
In contrast to snipers, DMs rarely work alone. While they can often act mildly separated from a main group such as sharpshooting from a better vantage point, they are usually in support of a main squadron. Some DMs can be confused as snipers, to clear things up, snipers DO NOT shoot on the front lines or run through the ranks and support a squad on the move. They almost always find a better vantage point and sharp-shoot from that location. Some DMs choose to use spring rifles and think that means they are snipers, what defines a sniper or DM is in their method of play.
DMs, just like their play style and guns, use apparel somewhere in between snipers and assault class. Sometimes players might use half cut ghillie suits to blend in with surroundings while also staying mobile.
3D suits are also popular because they are light weight and mobile but offer good cover. Another advantage of the 3D suits is the fact that they don't snag onto brush and thorns as easily as ghillie suits.
Sometimes, DMs will also play with regular flat camo such as multicam or digital but it is not as effective.