I think I have solved the "ammo problem" I was having with my UltraMag 50. Today I shot 26 rounds through it; 6 WW2 AP and 5 each four other kinds. All went off on the first try save one round of WW2 AP.

I looked at the primer of this round, and it was barely dented at all. All of the others had solid hits. I put it in and tried once more; it went off.

When I got home, I examined the bolt carrier and hammer and noticed the paint on the left side (where the bolt carrier release would be) of the hammer was worn off. Also, the paint in the same area of the bolt carrier is worn. Clearly, if the hammer is spending energy stripping paint, that energy isn't being used to motivate the firing pin.

Next weekend, I will try to replicate the light strike to test my theory. If it holds, I'll either need to put a mass on the bolt handle or polish away some of the bolt carrier. I'll let you know.

Sounds like you need to remove some metal from the raceway where the hammer is going on the Bolt.  I've never examined one in detail.  I wonder if you are over-rotating the bolt.  Perhaps the slot in the bolt is out of alignment because of over or under-rotation.  That could be solved by sleeving the bolt instead.  You might also contact the maker and ask them for a solution.  Just a phone call away.

we have discussed it in this forum. I have yet to do the testing - I want to buy some primed brass and see what the critical angle is for engaging the bolt and getting a light strike.