1/2 way Cr. Charlie,
Capping on the clock only occurs where there is a call for a RELOAD on the clock. 99% of the time it is a stage where you cap at the loading table.
Here's an old posting of mine regarding cappers:
For the Colts just about any in-line capper will do. I have improved upon them by grinding off a little of the tip of the spring that protrudes beyond where it holds the cap. The brass part opposite the steel spring is also ground back some so the capper can be placed directly over the cones (the polite Victorian term for "nipples"). The grindings eliminate the extra metal that gets in the way of fast capping on the clock.
For the Remingtons, the Ted Cash in-line capper is best because the two thin steel springs that hold the cap in place will fit into the tighter cylinder/cone cutout better. I also grind off the extra spring steel that sticks out beyond the cap. The brass part under the cap on the Ted Cash in-line cappers tends to bend back when capping in a hurry and is the only weakness in the design that I have seen. The cheepo cappers from McGees @$3.90 [no longer in business] each work fine for me after grinding.
As for the teardrop cappers, I keep dropping caps out of them and losing caps in the gravel at the range. When they work, they work well.
I keep an in-line capper and cone pick on a cord through my vest button hole for on the clock "reloads".
Black Jack, see all the tricks to the trade you can learn just by the asking? I keep giving away all my secrets and more and more folks like to shoot the per-cussin' revolvers and I get beat more and more but you know what? I feel like a preacher giving the Word of the Lord to others and then hearing them go on to preach a better sermon. It can't get better'n that! I've been accused of being a little "tetched" but I don't get foam in the corner of my mouth when talking Cap&Ball (yet).