I decided to quantify the results of "reloading" a Large Pistol primer with toy paper caps obtained from Amazon.
I levered out the anvil with a small nail, flatted the firing-pin dent as much as possible by using a flat punch inside the cup. 2 caps were used per primer, cut out with a leather punch.
I then dropped the cap-primed cup into my priming tool, raised it up a bit and dropped the anvil into the cup - and gently pressed the primer up in place in the brass to let the anvil find its own center in the cup.
Case primed:
I shot regular Win LPP versus these toy caps a few weekends ago - load was 4.1gr Clays under a 230gr RN cast. Here are the chronograph numbers:
No failures to cycle or fire - but other than the obvious smell difference (caps are very distinctive), I did notice a very tiny delay between the click and actual bang, which I guesstimated at 1/20th second:
So, I saved the audio from that video as an MP3 and opened it in an audio editor, Audacity - using that I was able to zoom in on the timeline and clearly saw the sound of the hammer-fall followed by a delay then the gunshot:
0.04 sec delay = 1/25th of a sec, so I was close with my earlier 1/20th guesstimate.
In conclusion, this can be done if needed - not a quick method but it's doable.