Have you actually tested original period caps in modern reproduction guns or is this a theory passed about ?
I have, indirectly. I grew up occasionally shooting originals, loaded with components my family had had stashed since the 1870s. I inherited several boxes of caps, and tucked these away for a rainy day.
Around 2007 I was shooting in some serious matches, using modern components and repro pistols. I noted I had problems with caps tying up the revolvers (something I'd seldom seen with originals and old components). I also thought the ballistics were a bit inconsistent. I set up a test to compare the old and new components, in original and repro arms. Guns were fired from a Ransom Rest; each round was chronographed. Guns tested were original Colt's 1851 Navy and 1860 Army, and repro 1851 Navy and 1860 Army from Uberti.
In the course of testing, I shot up ~500 original caps from sealed tins of Eley's caps marked "250 metal lined caps made exclusively for Colt's PT Belt and Pocket Pistols". I compared these with modern caps from CCI, RWS, DGW, and Remington.
Out of ~500 shots with the Eleys, no caps fell off prior to shooting; four fired caps came off when the gun was cocked for the next shot, resulting in tie-ups that had to be cleared to continue. All happened with the same gun--the Uberti Navy--and while I always meant to test to see if it was the same chamber, I traded the gun before I got around to it. Of the modern caps, the RWS were the winner for reliability, with only a couple falling off during rotation, and IIRC, about 20 fired caps coming off when the hammer was cocked. The other brands resulted in more functional problems. No Eley caps failed to fire; the others all had a few misfires. For consistency in velocity, the modern DGW caps were #1, Eley was #2, and RWS was #3.
When the Eley caps were made, they were an important component of a weapon system that people relied on for their lives. The military here and in other countries bought millions of caps, tested them for consistency, and rejected any lot of caps that exceeded their standards (which were much higher than we accept today!). There is no reason to think today's caps--made in relatively small quantities, for folks playing games and plinking--would somehow be better. The only advantage to modern caps that I can see in that they are less-corrosive, but I'd gladly accept the need to clean more carefully in exchange for the reliability the caps were designed for.
But that isn't an option. Things weren't perfect "back then": there were several patents issued in the US for cap shields, with some even being tested by the military. Overseas, there were other approaches taken, e.g. different designs of the recoil shield, etc.
I don't recall seeing patents etc for a cap rake. None of the thousands of accounts of use of Colts pistols as a primary weapon that I have read, or my own experience, suggests they were necessary with the caps then in use. The thin-bodied caps we have now have changed things. I fit the nipples to snugly fit whatever caps I can get, and any revolver I shoot in matches will have a cap rake.
