I recently purchased a WW Greener FH25 at an online auction, when I received it I found it had a single selective trigger. The serial number puts the date of manufacture between 1915-1920. I have not been able to find any information on the web about single trigger guns. Does anyone on here have any information about the single trigger? Is there anything I need to be careful of? I would post pictures but don't have a website to link to. Any information would be appreciated, thanks in advance.