wolves3012 said:
Yes and no. Using a card to guide the film in puts a lot of pressure on the plate springs, pressure they were not designed for. You risk flattening them and consequently reducing the pressure they exert on the film that keeps in within the guide rails. Too weak and the film can ride out of the gate and get tangled in the innards. I have a FED 1 (granted not a Leica, but essentially the same in this area) which appears to have suffered in this way. I had to re-tension the springs and yes, they are indeed quite delicate."
The Leica pressure plate springs are flat springs, about 5mm wide and 25-30mm long and can deflect only about 1mm when pushed all the way back. It is difficult for me to imagine any damage being caused by the insertion of a business card. I'd hesitate to extend experience with a Russian camera too liberally to a Leica. My experience with Russian camers (and I have more than one) is that they often have all sorts of manufacturing and materials defects in them.
YMMV, of course
Well, I think we'll politely have to agree to disagree. I'm not going to poke cards into my Leica when the proper method is quicker and less risky. Nor am I going to say you can't do that if you want to.
As for extending the Russian camera experience to a Leica, I did say "granted, it's not a Leica". I have upwards of 20 Russian cameras and I'd certainly not class any of them as akin to the obvious engineering of a Leica. That said, none of them has manufacturing defects (bar a late FED 5C where the self-timer fails to trip the shutter, due to a too-short operating rod). They're roughly made, yes, but they all work properly after a bit of fettling (Leicas need that too).