After a detail cleaning of the FCG with WD-40 and compressed air, and the parts relubed with CLP,

We need three photo's,

The first is the condition of the disconnector sear edge,

The second is the condition of the back sear on the hammer that mates with the disconnector.

The third is a photo of you lowering the hammer back to get it rear sear as close to the disconnector sear without touching the trigger.  So need a photo like this,



Bluntly, could be crap in the FCG that has collected over the years that needs to cleaned out, a worn out disconnector spring, or just a worn out disco that the free gap is now too large instead.

Looking at the photo I posted, what I need to see if the gap between the hammer back sear, and the disconnector front sear when you cock the hammer back to get the rear hammer sear in line with the disco sear.

Being that the rifle is a SP-1, will bank that the disconnector spring needs to be replaced for starters, and just want to see if the disconnector needs to be retimed (just take a few mins), or the replaced instead.

Bluntly, where is what is going on.  You fire the rifle, and instead of the disconnector holding the hammer back until you release the trigger again, the hammer is being release from the disco with the trigger still held back, and rifle is doing it normal safety feature; which is the hammer not held back by the disco catches the firing pin collar to hold the bolt from locking up and preventing slam fire.

Free Gap looks huge, but lets weed a few thing out,

Hold the hammer steady in place un-cocked, and using a punch, punch out the hammer pin from the receiver, then lift the hammer out (again, hold the hammer steady as you punch the pin out so the hammer not trying to cock to one side to bind the pin from smoothly punching out of the receiver).

Hammer removed from the lower, push the trigger pin out.  This will allow you to lift the disconnector out of the trigger.

If you can not maneuver the trigger past the selector to remove the trigger, with pressure on the ejection side of the selector end pushing it in, flip the selector from safe to fire and back again.  With enough pressure on the ejection side of the selector, this will pop the selector  detent pin tip out of the detent channel and the selector can be removed for the receiver. If you are having problems removing the selector this way, you can remove the pistol grip but make sure to pull and place the sector spring and detent (will be up in the spring channel) for safe keeping.

Now, as you are pulling the parts, what you are really looking for is anything that is holding the front of the disco up, instead of it seated tight against the top of the front of the trigger.

Now need photo's of the parts, including the disconnector spring removed from the trigger,
Note, disco spring installs large coils side down into the trigger, so may take a set of needle noise pliers to remove it.

As for new parts, let me see the condition of the old parts first.  With the age, the disco spring may need to be replaced, but in regards to the disco, may just be crap that is holding it open too far to cause to cause the huge free gap and/or it can be re-timed.

If the disco just needs to be re-timed,
http://www.ar15.com/forums/t_3_66/656984_AR_pistol_problem.html