FWB 300S rear sight puzzle

brians356 · Post by **brians356** » Mon Nov 09, 2009 12:57 am

My recent FWB 300S acquisition (serial number 136xxx) has a curious issue with the rear aperture sight. The sight is marked "Feinwerkbau Oberndorf", and will not tighten on the dovetail. There are lateral grooves across the top of the dovetail, and the sight has a threaded cross shaft with two diameters and a knurled knob for retracting to one side. Presumably the cross shaft is positioned over one of the grooves and the shaft screwed home so that the thicker part indexes in the groove as it progresses deeper across the sight base. But the dimensions are all wrong and it does not cinch up. With the cross shaft all the way home and tight, the base rattles around on the dovetail, fore/aft especially. It seems the dovetail itself is too shallow. I've worked on a lot of sporting firearms, and mounted a lot of scopes, but I am a bit mystified in this instance. I don't see how this system could ever really be secure even if the dimensions were spot on. I'm used to things clamping very tightly to a dovetail, but there is no real clamp at all here. Any help would be appreciated!

Brian Adams
Reno

JSBmatch · Post by **JSBmatch** » Mon Nov 09, 2009 3:46 am

Oil all moving parts/threads on the clamping screw. If this does not work then check there is not excessive wear on the back sight dove tails.

The slot in the clamping screw knob is so a small straight edge can be use to tighten it up, but this only normally requires just a tweak or a bit more than your fingers can do.
JSB

brians356 · Post by **brians356** » Tue Nov 10, 2009 11:32 pm

JSB, thanks, I really cranked it down using a slot-activation implement and it cinched. Not an elegant design for something made by (or for) FWB. It essentially distorts the base to squeeze the dovetail. But it does work. Thanks for the tip.

Brian Adams
Reno, NV, USA

JSBmatch · Post by **JSBmatch** » Wed Nov 11, 2009 9:23 am

Hey
I've got all your records, just fooling.

Just make sure the clamp screw and all parts are oiled.
You will notice a flat on the inner shaft, this should be facing downwards when you slide the sight on. Once you eye ball it over one of the grooves, tighten up and it should swivel round into the groove locking it in place.
JSB