Caps

[Blackfeet]

New nipple, never dry fire (with hammer strike), caps seem to fit well.
I too doubt that it is primarily degradation of the springs if the materials, geometry, and heat treatment of the springs are correct. A quality control issue of even one heat treat batch at the manufacturer of the springs could easily be the case and does not necessarily reflect badly on the gun brand. There appears to be enough history here to say that there has been something amiss at times.

[Blackfeet]

Squeeze, to be clear, you have valid points and I did not mean to seem dismissive, but in this case that is not the issue. I suspect that as Mongrel has also stated, a simple batch of iffy springs can easily be the culprit. The simple spring is a high volume and inexpensive part in the larger scope of things and likely does not receive the attention that it deserves.

[mongrel]

And to second Blackfeet, in the three cases I referred to, the mainsprings were weak. In the case of the really bad one, new nipples of several types were tried, with no improvement -- and I doubted when I tried them that there would be any improvement, because the weakness of the mainspring could be felt when the gun was cocked and seen when the hammer fell. I am not exaggerating when I say it fell so weakly/slowly that the eye could follow it going through its arc.

In the majority of cases, though, it is correct to focus first on the nipple and eliminate it as a possibility before looking to other causes.