TIANJIN, Jan. 2 (Xinhua) -- A Chinese woman who ran a small recreational shooting gallery in northern China's Tianjin municipality has been sentenced to three and a half years in prison for illegal gun possession.

The sentence shocked the public and caused widespread debate about the criteria for legally defining guns.

Zhao Chunhua, 51, moved to Tianjin to live with her daughter, and opened a roadside shooting gallery to help her family but was arrested in October. Among the model guns seized from her stall, six were identified as real guns by police.

Zhao's daughter believed they were just toy guns using plastic bullets to hit balloons, and said she would appeal to a higher court.

According to a 2010 Ministry of Public Security document on firearms identification, unauthorized guns able to fire bullets with a force of over or equal to 1.8 joules per square centimeter are considered illegal firearms.

The force of the six guns owned by Zhao ranged from 2.17 to 3.14 joules per square centimeter, exceeding the statutory standard, the court said.

However, the standard was soon criticized following the verdict. A netizen called XiaoL said even a self-made slingshot has a force of 10 to 20 joules per square centimeter, thus the legal standard is too strict.

Another netizen @Hongshui said that the 1.8 joules per square centimeter standard is too technical and vague a legal definition for the public to follow, and could easily lead to passive crimes.

"A weapon can be determined as a gun if it is able to cause serious injuries or blindness by shooting within 30 centimeters in the eyes of a person," a lawyer who once served on a technology department of a police station told Xinhua. "Based on the legal rule, we calculated the 1.8 joules per square centimeter standard."

The sentence was also widely questioned.

"Three years and six months for possessing six toy guns -- isn't it too heavy?" wrote netizen Yikesong.

Cui Jianhua, a lawyer in Beijing, said the key issue with the conviction was the issue of subjective intention, specifically if "she knew exactly that they were guns but still chose to possess them."

Based on common sense, no one would assume toy guns at a shooting gallery were real guns. Therefore, Zhao had no subjective intention, and it did not constitute a crime, Cui said.

But Yang Yueming, a lawyer in Tianjin, said as long as the weapons were regarded as real guns by the police, the owner should be punished according to the criminal law, which stipulates three to seven years in prison for serious offenders illegally possessing firearms.

"Legally the verdict is fair. But the court should also consider the defendant's potential harm to society and the social consequences of the case, demonstrating the law's role to educate and save," Yang said.

Zhao's plight echoed the case of a man in eastern China's Fujian province, who was given life imprisonment in 2015 for purchasing 24 imitation guns online. Police deemed 20 of the guns as real guns powered by compressed gas.

The provincial higher people's court ordered a retrial in October 2016after the case caused widespread discussion.

"The punishment obviously did not fit the crime," the court said.

With the weapon identification standard and injury force description as they are, lawyers have advised the public not to randomly purchase toy guns.