The Photosniper SLR-gun was made first by GOI and later by KMZ, originally for military use. Probably its original purpose was to use the quiet hands of good soldiers to shoot reconnaissance photos out of their emplacements. Later models were freely available as cameras for amateurs, nature photographers, spies and paparazzi. (camera-wiki.org)

Here's 3d model of Photosniper handguard and stock including inside mechanisms. Can be used with (beautiful) Tair-3AS 300 mm f/4.5 tele lens. Digital camera can be mounted with M42 adapter and trigger button is very easy to craft. (Trigger adapter can be supplied on request)