I bought a used Kepplinger trigger with side safety for my FN Mauser. For some reason the sear will not fully release when the trigger is pulled. The sear will release, but the cocking piece will only move about 1/8" and stop against the sear. Do I need to polish the rear edge of the sear to make more of a bearing surface, or is there something else going on here?

Thanks in advance

Try the "screwdriver" test. Pull the bolt, depress the sear with a screwdriver and pull the trigger. Does the sear drop clear of the opening? If not you may need to relieve the opening a little with a needle file until the sear will drop completely through it, and then some.

If this is occuring when installed I would look to see that the sear has clearance through the receiver. Sopmetimes you need to open the sear hole up a bit and sometimes you need to shim between the trigger housing and the bottom of the receiver.

The cocking piece on the FN may be the trouble as well if it is commercial style and not the more common military style cocking piece.

Good double entenre Malm!

I love to see folks learn to work on guns, but when it comes to safeties and triggers it is often best to learn by watching someone who knows what they are doing. Would hate to see you create an unsafe condition

Well, the seller offered to take it back and try it in his FN mauser to try and see what the deal is. The receiver doesn't seem to be interfering with the sear at all.