(nowadays the SIG SG 550), and the going rate for civilianised Stgw. 57 rifles on the private weapons market is reported to vary between 300 and 500 Swiss francs. In Switzerland, the Stgw. 57 is also used for target shooting matches. For this the standard iron sights can be replaced by target shooting diopter and globe sight sighting lines. When the original sighting is kept Swiss sport shooters refer to a such unmodified rifle as Stgw. 57/02 (small diopter allowed, but no globe sight). When a globe sight is added and possibly the sighting line radius is lengthened by mounting the globe sight nearer to the muzzle it is referred to as Stgw. 57/03. As of 2017, original military barrels, which are known for longevity and are rated for up to 15,000 rounds (for later nitrided variants), could be replaced by match-grade barrels. Other upgrades include improved target sights, mirage bands, lighter hammers, custom pistol grips, custom barrel jackets and regular replacement of bolt components. SG 510-4 (7.62×51mm NATO variant) The SG 510-4 chambered in 7.62×51mm NATO was adopted by Chile and Bolivia. Compared to the SG 510-1, the following main changes were applied: Lighter, shorter (505mm) barrel with 8 (early), or 16 (late) chamber flutes, 304.8mm (1 in 12 inch) twist rate Revised delay angle on the bolt carrier wedge Straight 20-round box magazine with feed path insert to accommodate for the shorter cartridge New low-profile iron sights, with ramp-adjustable rear sight aperture and semi-hooded front sight Spring-loaded detent on the front barrel jacket bushing/front sight base for rifle grenade sight Angled stock tube and stock assembly, with correspondingly modified recoil spring assembly and bolt carrier tail Walnut wood stock and handguard New pistol grip design (after ca. 1966) Lightened roller recesses and winter trigger Simplified bolt carrier with add-on, unified rubber buffer and charging handle lug The SG 510-4 is officially classed as an automatic rifle but also served as a designated marksman weapon (in Chile with Supra 4×24 scope) Variants AM 55: Original version as adopted by the Swiss Army as "7,5mm Stgw. 57". SG 510-1: Export model of the AM 55 chambered in 7.62x51mm NATO. SG 510-2: Lightened variant of the SG 510-1. SG 510-3: 7.62×39mm variant with shorter barrel, receiver and barrel jacket. This was produced in small numbers as a prototype and submitted to the Finnish Army. This model of the rifle was never