I have had my 853c (and a couple of other fine 10 meter rifles) for about three years now and I have yet to fire a prone shot...
It took me about four months to get five in the black (on cadet grouping targets) consistently from kneeling.
I agree that bench resting at ten meters is not a lot of challenge. So I shoot standing offhand most of the time.
I have started using sidewalk chalk cut up into peppermint sized discs (as was suggested by another member).
I also use bottle caps stuck on edge in plasticine.
When I get warmed up and am on a roll I use yellow map pins.
But if you really want a ten meter challenge get a pistol....I just got one a couple of weeks ago and I had to start with the bottom of a gallon paint can, then a coffee can, then a bean can, then a tomato paste can....now I'm down to chalk and bottle tops but only hitting one in three...not too bad considering I have tendinitis that needs physiotherapy in my right elbow. My hat is off to the guys who can consistently smash aspirins standing offhand with a pistol.
Then if you want to increase the challenge get a clock and limit your lock load and aim time to 30 seconds per shot.
My personal best so far has been thirty bottle caps in a row on the clock standing offhand with the Daisey 853c. That was with preloaded five shot clips and I don't think I could match that in single shot.
On the thirty first cap I was shaking from lactic acid build up in my arms and the cap didn't go flying. I fired three shots and gave up. Later I noticed that the cap had three dents in it.....
I know I'm going to be handed my butt the first time I compete, but I am going to train and practice to do my best.
"Aim small miss small"...and when you're done doing that...aim even smaller.