ive got a nightforce 5.5-22-56 that was suposed to come from the dealer where i bought it with a set screw under the elv. turret for use as a zero stop.i dont think it did but it has a set screw in the middle of the brass turrets under both the elv and wind turrets.is this on all nightforces and what is it for?this is the only nightforce i have ever had so im not sure if it's factory or what.thanks for any info.