I am a bit of an air gun nut, graduated to the top of the springers being a tuned Diana 52 Luxus. Then moved on to the PCP's, started with an Air Arms S510, accurate, powerful, but not in the high quality stakes. Then came a Daystate Regal, better in my opinion, very accurate, but not quite there yet. Finally I bit the bullet, or pellet in this case, and got an FX Royale, rotary magazine, carbon fibre air reservoir the lot. Put a Swarovski z5 scope on it with the coloured ballistic turret calibrations, parallax adjustment. Opted for the high grade walnut stock too. WOW, at last, this is perfection! This set up is so accurate it is scary, with precision shots to 100m a breeze. It is super powerful too. You learn a lot about trajectory with an air rifle this good because you can predict its performance. As to calibre, i have 0.177, 0.20 and 0.22. The 0.22 in these modern high power PCP's will get to about 35 ft lbs without going supersonic, which is plenty power for small game hunting like pigeon, rabbits, squirrels etc. This set up is expensive, but you will not be disappointed.
