The youngster walked free after Judge Roger Chapple told him his "hands were tied" and he could not impose a custodial sentence, only a youth rehabilitation order.
The boy had admitted to having two pistols and 13 bullets hidden under the floorboards at his house in Manor Park, East London.
Sitting at Inner London Crown Court, Judge Roger Chapple told him: "The courts generally take a very serious view of this sort of thing and mark it with long prison sentences.
"As it is, parliament has tied my hands. I have no power to send you to any form of detention."
If the boy had been 16 or over he would have been locked up for a minimum of three years.
Legally, he said, it was "impossible to come to the conclusion" that the youth was a danger.
The Ministry of Justice commented that sentencing guidelines are set by an independent body, adding the boy had not been found guilty of intending to use the guns.
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