TC Omega + William's peep = not hitting paper...

[DeerMeadowFarm]

I purchased a WilliamÂ’s receiver (peep) sight for my Thompson Center Omega. It came with WilliamÂ’s fiber optic sights from the factory; in fact, the ramp portion that mounts to the barrel was identical in height as the factory sight. A peep sight works best if you can get it closer to your eye and further away from the front sight so I mounted it in the two scope mounting holes that were furthest back.
Before I took my original rear sight off I tied to adjust the peep to be in line with the factory sight as I had the factory sight adjusted perfectly. What I found was I had to raise the peep sight so high that a quarter of it was hanging off the front of the ramp. I figured I was doing something wrong so I adjusted it back down so it matched the same graduation mark I had the factory sight set at.
Well a trip to the range confirmed my fears. At 25yards I couldn’t get it on paper. Of course the cardboard and plywood scraps at the range were so shot up I couldn’t tell where I was hitting. I took a fresh piece of plywood and stuck a target with an 8” circle on it. My first shot was at least 6” below the target. I adjusted the sight up until 1/3 of it was hanging off the front of the ramp and this only brought me within two inches below the 8” circle.
Obviously, this isnÂ’t good. When I got home I tried to put a straight edge to see if the barrel tapered down towards the breech from the point where the factory rear sight was installed but I couldnÂ’t confirm that. IÂ’m thinking it has to be the case however as the ramp portion of the factory and the peep sight are identical in height. It also appears that the bottom of the notch in the factory rear blade is the same distance as the center of the peep sightÂ’s orifice.
I bought the peep sight from CabelaÂ’s and because they didnÂ’t offer a shorter front blade with it as a set I assumed I could use the factory height front sight. A quick check of the WilliamÂ’s catalog does not list a front sight change as being needed when using the receiver sight.
So what can I do at this point?

[bustedknee]

Obviously, there is a difference in in height in different rear sight locations.  By moving the rear sighting point back the relationship between sight plane and trajectory is affected.

You need a new front sight.

I've been through this several times.

Measure, measure, measure, calculate, calulate, calculate, then order the three height sights you think should work. 
Send the two, that don't work, back for a refund.  Or hold on to them for the next project.

[oneshotonekill]

Are you using a monte carlo stock on the Omega.  Although I believe you are going to need a different front sight to solve the problem, part of your trouble may be the position of your eye in relationship to the sights due to the height of the stock.  Now your rear sight is much closer to your eye, with a high comb you may be tiliting the gun down to get a proper sight picture.

[captkev]

 Great info guys, I'm about to go into modifications on a NEF and all this info will help me get things right, I'm clicking and reading anything I can find on site changes for my gun.