I'll bet the print on everything you read was larger then, too.
1. I was playing with caps for quite some time before I learned to read, although that was at a normal age.
2. My recollection is that roll caps used to have noticeably raised bumps containing the gunpowder. The caps I have been able to obtain in more recent times for both my sons are much flatter, contain less powder, and therefore do not make as loud a bang.
3. "The revision of the US Standard Consumer Safety Specification for Toy Safety ASTM F963-07, which became effective in February 2009, among other issues addresses the maximum noise level for various types of toys, including those for cap guns.
"... the maximum impulsive sound level measured at a 50 cm distance from the ear is established at 125 decibels (dB). "
4. The previous CPSC regulation required that the maximum allowed sound intensity for caps was 158 decibels at 25 cm. This is equivalent to 152 dB at 50 cm. This regulation is no older than 1973.
5. Some websites which discuss cap guns which I consulted indicate that caps used to contain on the order of 0.20 grains of powder. This ad from an online toy company says that their ring caps contain less than 0.002 grains of powder.
You’d get more noise from a mechanical snapper.
I have to admit, I admire the sheer gumption of it, though. "Oh, you doubt me? Well, here's just a little evidence I know what I'm talking about... (THUD!) So there!"