I think your perception of mamluks or in Arabic مملوك, which literally means "owned or something owned", is slightly tainted by your connotative definition of slaves and slavery. If you are basing your ideas about slavery in this particular time period and region and culture on the institution of slavery practiced in the Americas by colonizers and subsequently Americans, you will not imagine a strong fighting force. However, the mamluks were bought or captured from pre-dominantly Christian families and were ethnically Georgian, Circassian, and Caucasian. They were brought to Egypt at a young age and Islamicized. As Muslims, they composed an elite warrior caste that followed a strong moral code and practiced religious/spiritual piety, not all that unlike samurai. They would later rise to political power and serve as rulers within the Fatimid caliphate. Simply put, they were effective in battle because they were trained to be. They were elite and professional soldiers. That was their original purpose. As to the techniques, tactics, equipment, and training that made them effective perhaps someone else would be able to share that and provide light on.