If you ever look at the underhammer guns, you will be shocked, perhaps to feel how much less Tension the mainspring has to ignite those caps or primers. Most of the mainsprings on sidelocks are too strong. And, You don't need much tension on the spring for a mule ear lock, either, to ignite a percussion cap.
IMHO, its the excessive force-force beyond that needed to fire the caps-- that contributes to barrel vibration, and possibly the movement of the sight picture away from the POA on any percussion gun. 10 lbs- less if the hammer weighs a lot-- is all that is needed to fire the caps on most all actions. The length of the fall of the hammer also is a factor to be considered in determining the force actually delivered to the nipple.
Some target shooters increase spring tension, so they can shorten the hammer fall, or " Travel", trying to gain the edge that short stroke firing pins give in target guns.
IMHO, shortening the fall or " travel" of a percussion hammer can not be done enough to speed the " Lock time" enough to make it worthwhile. That additional force created by using heavier springs bashes the nipples, and rattles the barrel, as any heavy firing pin spring does in modern guns. Considering the ignition speed of most locks, even well tuned, and the slower speed of burning of Black powder, Lock and barrel time are not improved by increasing spring tension and shortening the hammer fall.
More important, as this all relates to Relative Accuracy, is the fact that we now have locks and barrels that produce SDVs in the single digits, and we have guns capable of shooting extremely small groups at long ranges, Without the shorter hammer fall or increased spring tension!
As with much of what works with BP guns, in this case, LESS is, again, MORE! :shocked2: :hmm: :thumbsup: