I only made 8 rounds using different primers and 4 of them with the bullet the normal way, the other 4 with the bullet upside down.
And such first shots are not so well to measure accuracy, so that's something for next time. I only could see that the POI is much lower than normal (as expected) and I even had the feeling that the upside-downs were more accurate than the normals, but it's too soon to tell something about this.
Did I mention that this Trailboss did resemble somewhat like blackpowder to me? The smell, the black empty case, ...

And I forgot to mention that I use Lee's factory crimp on all these rounds. Not that it is necessary for single shot rifles, but I do believe it can improve accuracy.

Aloys, I crimp all my rounds. I have been doing a side project trying to determine the benefit of crimping. I've been loading shells then pulling them using a scale to measure force with the assumption that a crimp increases neck tension. I stopped using my Redding seating die's built-in crimp and got a dedicated Lee crimping die which as been an improvement because case trim length isn't critical. So far the results have not been that significant. My 6.8 loads average 9 pounds of pull force without a crimp and 11 pounds of pull force with a crimp, a 20% increase. The neck tension on my .270 Win is above 30 pounds of force because of its longer neck. However, there has been no difference in the .270 between crimp and no crimp. However, in both calibers, the crimped cases have had half the std dev in neck tension. I haven't measured for accuracy but this is reason enough for me to crimp.

SJ, should I become afraid now that we seem to agree on some matters?

For a long time I'm convinced that Lee has very good engineers, I often like the way they handle a problem. In my opinion Lee only should invest a little more in the manufacturing processes so that their quality improves. Think about your feelings when you have a nice designed italian car, but it doesn't start when it's raining or cold...

Aloys, Lee makes things simple and easy. It cost me more than a hundred dollars in competition dies to match the quality of Lee's little classic hand loader which cost me $25.

I think its my Nosler manual that shows benefits of reloading for accuracy using one of the old old old tap with hammer loading die sets......