The M107 fires the hugely powerful .50 caliber ammunition that has long been used as the standard Army Sniper

The M82 is a short recoil semi-automatic firearm. When the gun is fired, the barrel initially recoils for a short distance (about 1 in/25 mm) being securely locked by the rotating bolt. After the short travel, a post on the bolt engaged in the curved cam track in the receiver turns the bolt to unlock it from the barrel. As soon as the bolt unlocks, the accelerator arm strikes it back, transferring part of the recoil energy of the barrel to the bolt to achieve reliable cycling. Then the barrel is stopped and the bolt continues back, to extract and eject a spent case. On its return stroke, the bolt strips the fresh cartridge from the box magazine and feeds it into the chamber and finally locks itself to the barrel. The striker also is cocked on the return stroke of the bolt. The gun is fed from a large detachable box magazine holding up to 10 rounds, although a rare 12 round magazine was developed for use in the first Gulf War.

The receiver is made from two parts (upper and lower), stamped from sheet steel and connected by cross-pins. The heavy barrel is fluted to improve heat dissipation and save weight, and fitted with a large and effective reactive muzzle brake. On the earlier models the muzzle brakes had a round cross-section; later M82 rifles are equipped with two-chamber brakes of rectangular cross-section.

M82A1 rifles are fitted with scope mount and folding backup iron sights, should the glass scope break. The US Military M82 rifles are often equipped with Leupold Mark 4 telescopic sights. The M82A1M (USMC M82A3) rifles have long Picatinny accessory rails mounted and US Optics telescopic sights. Every M82 rifle is equipped with a folding carrying handle and a folding bipod (both are detachable on the M82A3). The M82A3 is also fitted with a detachable rear monopod under the butt. The buttpad is fitted with a soft recoil pad to further decrease the felt recoil. M82A1 and M82A3 rifles could be mounted on the M3 or M122 infantry tripods (originally intended for machine guns) or on vehicles using the special Barrett soft-mount. The M82A1 can be fitted with a carry sling but according to those who carried it in the field, the M82 is too uncomfortable to be carried on a sling due to its excessive length and heavy weight. It is usually carried in a special carry soft or hard case.

The M82A2 differed from M82A1 mostly in its configuration — that the pistol grip along with trigger had been placed ahead of the magazine, and the buttpad has been placed below the receiver, just after the magazine. An additional forward grip was added below the receiver, and the scope mount has been moved forward too.

It has been erroneously cited that the maximum range of this weapon (specifically the M107 variant) is 6,800m. This is, in fact, the distance as quoted in the owners manual that should be allowed downrange for bullet travel. .50 calibre rounds and above have the potential to travel great distances if fired in an artillery-like fashion, necessitating the observance of large safety margins when firing on a range.

The Barrett M82 has been seen in a number of Hollywood action films (e.g. Navy SEALs, RoboCop, Miami Vice, Smokin' Aces, Shooter, Rambo), often depicted with exaggerated capabilities. Misconceptions include being able to shoot down airliners; while the M82 was designed to disable parked aircraft, it is extremely unlikely that even the most highly trained marksman would be able to bring down a flying airplane firing the entire 10-round magazine, let alone one shot.