None of my reproduction Colt "Cap-N-ball" revolvers have excessively hard to cock hammers & I've never had a problem with them firing a percussion cap. In fact none of the percussion long guns I have had any dealings with have seemed to have springs any stiffer than those found in a normal break open sporting shotgun, except possibly Military Muskets etc. Some of those have truly massive locks, including powerful springs.
On a Lefever Arms Co hammerless gun with in-frame ejectors (Far & away the most often found LAC ejectors) the Main Spring does dual duty. They have V springs & the lower limb powers the hammer while the upper limb powers the ejectors.
