The issue is, every now and then (only twice so far, but that is too much) the trigger guard will pop out, and with the hammer being cocked, the guard then falls fully open, and then the whole assembly drops half way out or falls out.  Now the stock pulls away from the reciever.  The gun just starts field striping itself in my hands.  Maybe it likes me.

Odd cause I  replaced the trigger guard after I ought the gun (used), and it is locked in place snug like.

Well, if anyone has ideas...

what type of stock?

Assuming you're talking about an M1 or a M1A, the "usual" problem is a trigger guard thats lost it's spring tension from being bent, or from age.

If the guard is either sprung or the latching tip is worn, the guard won't lock properly.
It  usually pops open under recoil, but in some cases, just pops open on it's own.

Milled guards CAN be slightly closed by CAREFULLY tapping with a rawhide or rubber mallet, BUT, be very careful because they are HARD and will break easily.

Stamped guards can also be bent, somewhat easier.

If you try to bend the guard, remove it from the trigger group.  Put the front of the bow on a wood table edge, and GENTLY "Bump" the rear of the guard with a mallet.
Bump it a little too hard, or bump too much, and the guard will snap in half.

The best "fix" of all is to just buy a new trigger guard.  
Usually the guard is worn out, and bending is a temporary fix at best.  
If the locking tip is worn out, bending won't help.

Quoted: what type of stock?

Like New Synth from Freds

And.. I did replace the trigger guard!