May be a self-made (collected from sec hand parts) rifle
Dont recollect any STs with scoperails. Only normal mk3s.
I do think there were early ones without theST name on it?
Army is only related to the Osprey ST. I think seller relates to this as both the mk3 and Osprey were both sold with 'normal' anschutz sight as well
If not sure its a ST, I would buy it