270 mm (1 in 10.6 in) 4 groove rifling. At the end of the barrel an integral long muzzle brake/flash hider is fitted that reduces recoil by about 25%. A rifle grenade-launching interface is also integrally machined into the body of the barrel. The barrel is surrounded by a perforated tubular aluminium barrel jacket with two spring detents for a sliding, underfolding integrated bipod—one near the muzzle to reduce shot dispersion during automatic fire, and another nearer the receiver and balance point offering more flexibility in the rifle role. The Stgw. 57 bipod legs are marked for use as an inclinometer for aiming rifle grenades at various ranges with and without an additional booster-charged rifle grenade. For such indirect rifle grenade fire, the Stgw. 57 was set on the ground and a weighted string attached on the sling loop was used as a plumb-line to set the correct firing angle reference mark on the appropriate bipod leg (left for boosted, right for unboosted). Swiss army knives were used as a makeshift plumb bob at the end of a string. Trigger mechanism The trigger mechanism has a three-position fire selector switch that is also the manual safety toggle that secures the weapon from accidentally discharging. The user selects the operating mode with a large side lever on the left side of the trigger pack that can be rotated to select S (safe), E (semi-automatic fire) or M (full-automatic fire). On the right hand side of the rifle, there is a foldaway 'winter' trigger which enables the operator to use the rifle with arctic mittens. It is also used for rifle grenade firing to avoid recoil-induced hand injuries. Sights The Stgw. 57 has a straight-line stock design, and an elevated iron sights line with a relatively long sight radius. Both the front and rear sights can be folded down when not in use. The rear peep sight of the Stgw. 57 can be adjusted from . From the sight adjusts in increments. From in increments, and from in increments. For low-visibility use, a reversible clip-on diopter with two self-luminous tritium-powered inserts (later carbon-14, one-side only) fitted laterally on each side of the aperture was issued. This element could be clipped by the user on the standard diopter. The front sight hood contained a permanently attached single strontium-90 or tritium-powered insert above the post to complete the low visibility sight line. When not