S&W 500 Lite Primer Strikes Help ?

Asking for advice on an issue with a S&W 500 Mag, 8-3/8" barrel SN CHH15XX, 2004 manufacture I think, I bought it new in 2004. It's had roughly 250 rounds through it, all but a dozen or so have been hand loads using 440 grain gaschecked LFN pushed by 14.5 grains of Tightgroup and Alcan Rifle Primers. I've used the same bullet, charge, and primers consistently. Three different people have fired it using that load and no one has had any issues up till now.

Yesterday, I loaded half a box of rounds and took it to the range. First cylinder full, it failed to fire every round although the primer was dented on each case. I tried lining each round back up and firing again, maybe 1 out of 4 shots would fire on the second time around, nothing after that. Made no difference whether I was single action or double action, same issue. I tried some more rounds and was able to fire maybe 1 out of each cylinder full.
Since the primers I am using are quite old, I suspected an issue with the batch of primers I had used and broke all the unfired ammo back down. Cleaned the primer pockets well, installed new primers from another batch, Tried firing the brass in the pistol but had the same problem, i.e click, click, click.
Took some other once fired brass and installed new CCI Large Rifle primers and tried them. Click, click, click. Same problem, occasionally one would go off, maybe one out of 5.
I tried some of the ALCAN Large Rifle Primers I had used originally in some rifle cases (I don't have any other platform for the .500 S&W rounds) and every one fired first time. Same thing with the CCI primers.

I have now decided it's the gun, not my reloads. Unfortunately, I couldn't find any brass I knew had been fired from my gun to compare the primer indentions with. Those that fired are considerably deeper then those that didn't fire but I would expect that.

Cleaned the gun, sprayed break free into the firing pin area and worked the pin back and forth. used a needle oiler and put some Rem Oil in it. The firing pin appears to be free traveling, no hang ups or stiffness and I could see the pin protruding from in front of the recoil shield.

Loaded 10 rounds with both types of primers and tried again. Click, Click, Click. But, on an impulse, I held the trigger all the way back while holding the hammer and released the hammer (Kinda like Fanning a single action) and it fired. It almost always fires when I do this. But it wont fire reliably either double or single action normally.

I know these pistols had an issue of primer piercing and broken firing pins early on and that's why they changed from Large Pistol to Large Rifle, I examined the end of the firing pin and it does not appear to be broken, it's nicely rounded and protrudes quite well with the hammer down and the trigger pulled.
I checked the lousy IL lock operated it back and forth to see if there were any issues with it, still no joy.

Do I send it back to the Mother ship ? Keep blasting it with break free?

I have not adjusted the strain screw since I purchased it, not even sure whether it should go in or out or even if it would make a difference. I'm hesitant to make any changes since the gun operated fine up to yesterday, no warning, no gradual failures, just click, click, click.

Any insight would be appreciated

Thanks
Dan R