Double taps

My Nelson conversion on a dedicated lower started double tapping this past Saturday at the Sectional, it's never done that before. The only thing I can think of that I changed was the ammo. I've taking it a part and can't find anything wrong with it. Why is this happening ? what causes this ? any suggestions ? any advise on this is appreciated.
                    Skid

What is you trigger pull weight? 
Conversions can be really touchy when at 2#. I've found 2.25# to be minimum safe setting to consistently safely function without hammer follow or doubling.
Middle sear spring leaf pressure is culprit as well.
Jon

Thanks Jon I believe the trigger is set at 2.5 lbs. So maybe a increase on the middle finger on the sear spring ?

Skid wrote:Thanks Jon I believe the trigger is set at 2.5 lbs. So maybe an increase on the middle finger on the sear spring ?

That would be my first try.

Assuming high end ignition parts? Drop in or gunsmithed?
Jon

These ignition parts are high end and gunsmith installed.

Probably a sear spring issue then
Jon

Thank you very much Jon.

Jon Thanks adding some tension to the sear spring fixed the issue. I did weight the trigger wouldn't lift 2 1/4 lbs and now it will pick up 2 1/2 lbs. I shot a box through it and no problems thanks for your help.
                                                                                                      Skid