The spring doesn't seem to be hitting hard enough to ignite the cap ? I get about 70% to go off. I think this is a problem with these ML's as a pard has one and his seems weak as well compared to the Thompson inline he has.

Any remedies?

Have you disassembled the bolt? The "problem" is usually a mix of oil & fouling that's blown back into the bolt and slows things down.

If this is an early #11 or Musket cap ignition, then it probably has a load of crud in the bolt that slows the firing pin travel. If you have not taken the bolt apart and cleaned it, you should look there first. I have a friend who has let a few deer get away because he sprays his bolt with some form of lubricant, but does not take it apart and clean it thoroughly. Usually the gun will fire after the first trigger pull breaks the crud loose, but the deer is gone by then.

I'll take it apart and look, but the problem has been since the first firing.

do it anyway. I've had new guns arrive gummed up with partially dried oil, a mix of oil and dust, rust from bluing chemicals that didn't get completely removed, or even rust on nominally stainless parts.

If you keep doing what you're doing (nothing) you'll keep getting what you're getting (misfires). Gotta break out of the pattern. It may not be the answer but it's something you can to do start.

Fresh caps? You did not say if they were or not.