Trying to figure out what scope i have. Its a leupold 12x fixed

[Daz28iroc]

So there is a serial number that has letter G, which i believe puts it as 1999 build date. I thought it was picked up second hand around 1997 but apparently that cant be right.
Ive had it in a box since around year 2000 ish.
Its fixed 12x.
Has basic crosshairs.
Shot very well on my remington 700 .308.
Its pretty long and has a 40mm front i think.

 

[polaris]

Leupold M8 12x fixed are great scopes, have three of those.

 

[Daz28iroc]

So its a m8. Thats what i was suspecting.
Paid for it with a bottle of scotch back in the day. Great buy i think.
Hoping it will be enough to shoot out to 600. Its set on a 20 moa rail.
Was trying to set a zero. Appears that the target turrets have 3 holes holding them in place but couldnt get a allen key to fit. Are they adjustable?