I found a great place to set up on a 5 m high granite boulder but it was a long way from the warrens. A good chance to test the legs of the 204.
At sunset I got out there and got comfortable. Next challenge was to work out how far away the warren was without a range finder (Santa has since let me down again!). I cranked the Bushnell 4200 up to 24x and measured up a rabbit with the Mil Dot reticle, looked at my range card and the answer was 250 m. I scratched my head and did the measurement again, it looked heaps further away. Same result. Oh well, guestimate the wind value, back to the range card and chamber a round.
I squeezed the shot off and looked for the splash. Nothing. Oh well forget the fancy reticle, it looks about 400 m, lets try that. I see the splash about 100 m short. Next round and aim up again and the splash is closer but still miles away. The bullet was dropping about 4 Mil short and about 2 Mil wide with a wind that I estimated should have only been 1 Mil.

As a consolation prize, on the way home I caught 5 sets of eyes at the base of a granite outcrop with the spotlight. By the time I got the Tikka out and loaded, the fox cubs were making a run for it trying to scramble up the steep face of the outcrop. Balancing the rifle on the car door, with the spotlight in the left hand I managed to deliver the good news to 2 of them before they got over the top.
Just before I fell asleep that night I had the eureka moment. The Bushnell Mil Dot reticle is calibrated to the 12 x magnification setting and I was using 24x.

Next day I went out with the Winchester for some more walk around fun and while I was there, measured the height of a fence post in front of the warren and paced the distance to the warren from that.
Back onto my boulder that evening I did the measurement with the Mil Dot reticle using the fence post and came up with 520 m. Wind directly behind me, three rabbits sitting on the warren, range card said 2.1 Mil of hold over, so double that and lets go.
40 gr vmax loaded, 4th Mil Dot resting just over a rabbit and squeeze the trigger. I watched Buggs jump a meter into the air and run off. A hit! and I started giggling like a maniac

Back home (still grinning like an idiot) the wife nodded her head politely as I tried to explain how proud I was of myself (she doesn't care about guns, and certainly can't appreciate just how far away that hit was). So I walked over to the pub and the reaction from the boys ranged from "bull#@%t" to "get your hand off it". Only one thing for it, I'll go back tomorrow with the camera. I need evidence.
Buggs had expired about 20 m from where the vmax hit his chest so I put him back where I hit him for illustrative purposes on the warren. No exit wound and the amount of internal damage was about the same as a 22LR. Looks like I have found the maximum range for this round.

The set up.

The warren is under the dead tree.

The result. You can just see the boulders in the background.
Lessons learnt, fun had!