Snomad, the FN '49 very rarely slamfires. If it does, it almost always is because the rifle is USING too much gas (i.e., not VENTING enough).
The actual mechanism of this involves the bolt-carrier being sent into recoil at too high a speed; it strikes against the rear of that trough-shaped receiver, stretching it. The receiver acts as a SPRING, coming back to its normal size and shape, sending the bolt-carrier and bolt forward again at much too high a speed. Bolt picks up a round, chambers it, and the firing-pin drifts into the back end and ignites the primer.
Get it bad enough, it can fire out of battery. Results from THIS can be catastrophic.
THIS was the problem with the GLOBCO 555, which otherwise was a really nice rifle.
The problem is at the gas port.
So you CURE the problem where it actually IS rather than where you WANT IT to be.
Adjust the gas-bleed for safe, accurate, controllable shooting.
The 2-piece firing-pin was a pretty good cure for a problem which never should have existed.
I shall now go and take another pill.