Floyd Mayweather Shooting Cops Stumped ... Still No Suspects

It's only been 5 months since a gunman opened fire on Floyd Mayweather's entourage in Atlanta -- wounding his bodyguard -- but cops now tell TMZ Sports the case has essentially gone cold.

No arrests. No suspects. No leads.

As we previously reported, Floyd and his entourage were returning to the Intercontinental hotel in Buckhead around 3 AM on April 9 when someone sprayed at least 12 shots at one of the sprinter vans in the caravan.

Floyd's bodyguard, Greg La Rosa, was shot in the leg and was rushed to the hospital. Miraculously, none of the other 6 people inside the sprinter van were hit.

In the wake of the shooting, cops said it appeared Floyd's crew was specifically targeted -- though it's…