A student who survived the Florida shooting wants you to see how a single AR-15 bullet butchered his foot ... mangling it to pieces.

Kyle Laman -- who was inside Marjory Stoneman Douglas High when Nikolas Cruz opened fire and brutally murdered 17 people -- tells TMZ ... he damn near needed an amputation after a bullet pierced his right foot ... leaving a gaping and horrifying hole.

The 15-year-old freshman -- who will need at least 4 surgeries and a year of rehab before he can walk again -- described the excruciating pain he felt after waking up from one of his surgeries.

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Kyle's mom, Marie, used the TV show "The Walking Dead" as a way of describing her son's injury. She's adamant -- no one in America who isn't old enough to buy a beer should be allowed to buy such powerful ammo. The family has now started a GoFundMe account.