Corrected entry: After the escape from the camp Rambo sets a claymore mine trap. He then runs for his life and seconds later half the forest is leveled from the mine. Claymores are anti-personnel mines and have a kill zone of 15 feet; they don't have the explosive power of a 2-ton bomb.
Corrected entry: At the beginning of the film when Rambo is taking the good Samaritans in his boat to Burma, the woman talking to Rambo asks him "how he got into all of this." Rambo replies that he was drafted into Vietnam. However, during the first two Rambo films, it is stated several times by Rambo himself, Colonel Trautman, and even Murdoc (when reading over Rambo's military records) that Rambo joined (volunteered, not drafted) the Special Forces in 1964.
Corrected entry: Rambo has booby-trapped an unexploded nuclear warhead, said in the movie to be from WWII. When the nuclear warhead goes off he is able to outrun it, but the initial shockwave would have been impossible to outrun. Not to mention the nuclear fallout, intense 5000+ degree heat, and other dangers of nuclear warfare.