The Perforator is a unique Infiltrator. It has the same appearance as the standard Infiltrator. It does more damage per shot, has a higher DPS, critical chance, critical damage, but a higher AP cost and significantly less durability. The biggest differences are the reduced rate of fire; the Perforator fires 2 shots for every 3 shots that the Infiltrator can fire and the reduced spread (which makes the rifle functionally more accurate over a longer distance). This gun is equipped with a suppressor making it silent.
Although the Perforator is a unique Infiltrator, it cannot be repaired with Infiltrators, but can be repaired with assault rifles. This weapon fires two shots in V.A.T.S. opposed to an ordinary assault rifle that fires three shots.
InfiltratorThe Pitt (add-on) - A scoped, silenced and stockless version of the R-91 assault rifle, it functions similarly to the silenced 10mm pistol in that, while not as loud, it deals less damage than its roaring cousin.
Sim version Operation: Anchorage (add-on) - A sim-only version of the weapon which differs only in health (essentially non-degrading). It features a cleaner, less-battered texture with fresh wooden and darker metal areas than its wasteland counterpart.
The following is based on Fallout 3 cut content and has not been confirmed by canon sources.
Wanda - A unique R-91 assault rifle that was cut from the final game.
Alloy steel assault rifle Operation: Anchorage (add-on)- A variant named "alloy steel assault rifle" can be found in the data files for Operation: Anchorage. It uses the Anchorage-specific texture for the weapon, but aside from name and appearance is identical to the standard R-91 assault rifle. It is likely the weapon was intended to be placed in the armory with other "wasteland" versions of weapons found in the Anchorage sim, most of which were cut from the final version of the add-on; as such the weapon can only be accessed through the use of console commands.
End of information based on Fallout 3 cut content.