Brocock Sniper XR Magnum pellet choice

I'm thinking of trying the Predator Polymags (.25cal) in my new Sniper, but thought it best to ask first if anyone has already done so, with this setup. At $23 for a tin of 150 (plus shipping), it's a little pricey to just experiment. Any thoughts? It doesn't matter if they would fit the magazine well, as I probably would be doing single-shot-feed anyway. Also, how would they do for longer range stability ? Thanks in advance for your inputs.