The Hammerli Single came in 4 basic versions - straight grip 'kurz' Slant grip 'kurz' Straight grip 'lange' and slant grip 'lange'
The 'kurz' models can only use the 8grm bulbs. The grooved frames on the early Singles are heavier than the later slant griped frames.
In it's evolution the Single got a more adjustable trigger and the very last version was identical in all but name to the Master incorporating that models adjustable sight rail.Most 'Lange' versions that I have seen have the later automatic gas release cap fitted. Production period 1960s - 1970s

With the kurz barrel yours will be one of these two.

[IMG]MVC00008 by Mark Davis, on Flickr[/IMG]

Lange models- if you get the bug

[IMG]MVC00002 by Mark Davis, on Flickr[/IMG]