Zaky,
Since no one else has answered you I'll share my experiences. Generally speaking buckshot is a short range affair. Jeff Cooper, at gun site training always said that buckshot was a 25 yd round on human targets. Deer are about the same size. However I found that you could improve on that some.
I once had my gunsmith build me a dedicated buckshot gun. We started with a Remington 870 and he cut the barrel to 22" and installed a imp modified truchoke. Screw in choke tube. The best load I found was the 2&3/4" 12 pellet oo buckshot load. It would keep all of those pellets inside a man sized target at 50 yds. That's the best I've ever been able out of buckshot.
Regards,