The single selective trigger...

[Pa SxS]

It sounds like more of a stock fitting problem if the single trigger works just fine with the stock off. The alignment of the receiver body with the floor plate is critical for proper sear/trigger alignment. There are 2 long screws that go through the stock to secure the receiver to the floor plate. The big screw under the top lever that screws into the floor plate and the smaller long screw that goes through the floor plate and screws into the top tang, both go through holes in the stock. Over or under tightening of these screws could change the relationship of the triggers to the sears. Hope this helps.

[Autumn Daze]

Chuck nailed it....The relationship between the top tang and the floor plate tang is critical. A matter of a few thousanths and you will have problems. Believe me I know.....

[John Truitt]

Mr Bishop and Mr. Suponski both have it right.

Sounds like a wood fit issue. Many times with a new stock or one that is old the wood gets compressed allowing the top tan to come closer to the bottom/ floor plate. Like Mr. Suponski said even just a few thousands off and your single trigger will start doubling. The best way to figure this out is to take the stock off, make a jig that fits at the back tang and floor plate screw (this acts to keep the two seperated the correct distance), then reassemble the gun with the stock off. My bet is everything will function correctly.
I have had to do this to several of my guns and even have gone so far as to drill out the stock and glass bed the jig in place so it acts like a second vertical strut so as to avoid this issue in the years to come.
Another thing to look out for is several restockers will leave out the metal cylinder that goes into the stock at the top tang screw. (sorry I cant remember what this is really called).

Good luck,
John

[Autumn Daze]

Thanks John and I admire your politness....But you may dispense with the Mr.Suponski...That was my Dad....Please call me Dave....

[Pa SxS]

Well, I very rarely am called Mr. Bishop so I kind of like the sound of it. Young Dr. Truitt is just being respectfull of his elders, that includes you and me, Suponski

[Autumn Daze]

Thank You...Mr.Bishop....