I had the same problem with my new LRH and it think it was oil/grease that the breech plug was shipped with. Give the breech a good Hoppes going over, followed by a good soap and hot water bath. That solved my problem. Also, most people seem to have good luck with the plastic jacket set up, but I am having my best luck with the conversion (bare primer) set up.

Also, be sure and use a 1/8 inch drill bit after each shooting session to ream out the fire channel from the rear of the breech. You will be astounded how much fouling build up you get out.

And, of course, always pop a couple of caps off before each shooting session to dry out the breech plug/barrel.

Also, I have never used sabots, but if they are relatively loose, it may not ignite.