The SIG SG 550 series of rifles goes for being among the absolute finest military rifles ever built.

The working principle is based on the AK-47 with a gas piston and rotary bolt. Unlike the AK series of rifles, the receiver is made in two parts similar to the M-16. This eliminates the dust-cover and makes it possible to mount the rear sight at the rear end of the upper receiver and thereby get a longer sight radius than is possible with the AK system. Of course, the Israeli Galil which also is based on the AK has a rear sight mounted on the dustcover, which in my opinion is a less satisfactory way to do it. This cover needs to be removed every time the Galil has to be cleaned, and over time I don't think it will be able to hold zero. The trigger mechanism of the SG 550 series is not based on that of the AK series, and is the smoothest "out of the box" trigger I have ever encountered on a military rifle. The two receiver parts are made of stampings, with the barrel mounting block/locking piece and the butt stock hinge part made of machined steel. The butt stock of the later production model has been modified with a  breaking point so that the stock will break instead of warping the receiver should the rifle be subject to an extreme (over)load. This way the rifle will still be operable although it no longer has a butt stock.

In the above pictures, the difference between the new (left) and old (right) style stocks is clearly visible.

The rifle has a flip-up front sight post with a luminous dot that corresponds with two similar dots on the open notch aperture of the rear sight drum for night use. The rear sight drum has four apertures numbered from 1 to 4 indicating distance in hundreds of meters.

It also features a  winter trigger guard that pivots to either the left or right side so that the trigger is accessible with heavy arctic mittens and magazines that can be clipped together. This system was later used by Heckler & Koch on the G36 magazines.

The factory offers various military models ranging from the short SG 552 to the heavy barreled SG 550 sniper. The factory also offer a wide variety of accessories including scopes, scope mounts, blank firing adapters, hard cases, a 40 mm grenade launcher similar to the M 203 and also a complete line of semiautomatic sporter models for the civilian market, the latest addition is four versions with the receiver painted in either black, blue, red or clear coating.

SIG SG 550/II  fitted with a  custom built BR Reflex suppressor.

This particular rifle is an early version which has the old style butt stock and lower receiver.