I have similar Palma rifle build with single shot Swing action Krieger 30" long 13" twist ss match barrel, Anschutz open peep sights etc etc and out 200+ or so shots fired this year I was able one time to have a lucky group of five shots into 1-5/16" at 300yds in ideal weather. I wonder if I ever have that kind of luck again, usually I am good for double that or slightly less. I say one lucky group like that means nothing.
Means nothing....?
Or means everything. Those are extreme positions to hold.
Your best ever group means everything because its possible and once achieved is easier to repeat if you choose to believe it is possible.
When it comes to high performance for humans the final push to the top is all in the mind. If you believe it enough you can achieve it.
It's easier to believe in something and repeat it once its been done and it doesn't even matter if you are the one who first believed or achieved a new level of performance. The fact that it exists as a result is enough to inspire great things for believers...