One thing that is constantly misconstrued is the roles of characters, particularly infantry, in a battlefield situation. This post will help to categorize infantry better and help players understand what role they should fill.
The rifleman is the core of the infantry. He's a generalist who covers for other roles. The rifleman's main goal is to utilize the advantages gained by the rest of his team. If his team is heavy on marksmen or grenadiers, he should operate as a ghetto version of an automatic rifleman, providing suppressing fire so that his allies can do their job. If he is supported by an automatic rifleman, the rifleman becomes a marksman, taking down foes with accurate aimed fire. If his squad is thrust into a CQB situation, the rifleman can also quickly engage close-range targets much better than an automatic rifleman, marksman, or grenadier.
The rifleman should be armed with an accurate mid-range rifle with a burst or automatic fire capability. Automatic fire is essential; without it, he is a marksman and fills a different role in the team. Depending on the needs of his team, this weapon can be a 500 yard marksman rifle like the M16 or a 300 yard assault rifle like the M4. The assault weapon is better for CQB but limits his role as a marksman, while the longer, more accurate rifle is less effective in CQB.
In the USMC, the automatic rifleman is the center of the fireteam. This is because the USMC uses M16s, which are almost marksman weapons. The automatic rifleman is armed with a general-purpose machinegun or squad automatic weapon, and this allows him to lay down covering and suppressing fire for his squad. His role is to pin down enemy fighters so that the riflemen and grenadiers can get into better positions and destroy the enemy.
The automatic rifleman ranges from reasonable in CQB to terrible, depending on his weapon. A lighter squad automatic weapon can be fired from the shoulder, but is less accurate and more unwieldy to aim. A GPMG is basically useless in CQB as excessive recoil and weapon weight leads to lots of missed shots.
The DMR's role in combat is to get kills. He utilizes the tempo control from his teammates (armed with automatic rifles or light machineguns) to take any and all opportunity kills he can. With an accurized, semi-automatic rifle, he can deliver lethal critical shots to enemies at 300-500m and possibly up to 800m, depending on his weapon. The DMR is the center of the fireteam in the Army, as the assault rifles used help give him covering fire so he can take advantage of enemy movement and shoot to kill.
The DMR is useless in CQB. In most cases, he will need to use a sidearm to be effective at all, and sidearms are not very suitable weapons even in close quarters compared to a carbine or SMG. The DMR is also not a sniper, although in Rifts terms he would have the Sniper skill. A sniper is an assassin who shoots from a hiding spot and disengages before combat occurs at all. A DMR is a combatant who fights alongside allied troops with accurate and deadly fire.
The grenadier is a team member armed with a grenade launcher. He may use an underbarrel grenade launcher or a standalone, but his role remains the same; engage and destroy enemies who have taken cover. Enemies pinned down by suppressing fire are easy marks for the grenadier. An underbarrel grenade launcher is best for these situations, as he can use his rifle if the enemy is not pinned down. However, the grenadier is also excellent for breaking up enemy formations, and in this role a standalone grenade launcher is a much better weapon. Careful selection of weapon is important for the type of mission being undertaken.
Obviously, a grenadier with a standalone grenade launcher should not engage in CQB without his sidearm. Even with an underbarrel and a carbine, the grenadier's weapon is heavier and swings slower, making him much less effective in close quarters. On the plus side, a grenadier with a carbine is still more effective than a marksman or automatic rifleman in close combat.
Close Combat Specialist
Close combat is the least ideal situation for anyone to be in. At 300m, there is more margin for error and a lot more missed enemy shots, especially if they are not wielding good marksman weapons. In close quarters, getting shot is very likely to happen if you don't have the element of surprise.
A CQB specialist has to choose his weapon carefully. The ability to shoot through walls is both a help and a hindrance, as penetration can lead to civillian casualties. The best weapon choice is a good, accurate SMG like the MP5 that can be maneuvered easily and has a controllable full-auto function. Light carbine rifles like the M4 are also good, as they have a bit better penetration through doors and sacrifice little mobility. In Rifts, the best CQB weapons are those with very short range and penetration, as laser weapons rip through non-MDC walls making them very risky in urban environments. Melee weapons are also reasonable in Rifts, but it can still often mean giving up the first shot to the enemy in order to get close.
The CQB specialist's weapon is probably ineffective at longer ranges. The M4 is a great CQB weapon as it is also effective up to 300m when contacts are farther away. A MP5 or other submachinegun does not have that advantage.
The breacher is the guy who shoots off locks and breaks down the door. He needs a shotgun, although in Rifts pretty much any MD weapon will do the job. An ideal breaching weapon is a carbine rifle with a Masterkey, as you have the CQB flexibility of the carbine and the breaching shell in the Masterkey. If you come to a new door, simply load another breaching round.
A tube-fed semi-auto shotgun with a pump is also a great breaching weapon. If you come to a new room, feed your breaching round, pump the action to eject your buckshot, then shoot in the lock. Your next round will be buckshot, which gives the breacher great CQB capability. The disadvantage of this is that you only have a few rounds before needing to reload, typically around 8 or so. If he is armed with a mag-fed shotgun, he must spend a lot of time feeding a breaching round and ejecting the old one, making it less than ideal.
Like the grenadier, the breacher can be very effective or ineffective outside his role. A breacher's weapon is reasonably good in CQB just by necessity but at battlefield ranges, he will be ineffective if he does not have a carbine.