I know the reason. the bell people can ram in your article is a small bell,and it is made less than 10 years as you said. I mean the real old bell in bell tower, it is very heavy,it's the third- big- bell in china. It was built near 600 years ago.vistors can't touch it beacause it is a real historical relic.I looked up the information about the bell .it is a Ming dynasty bell.

As I known, The bell in bell tower is not Qianlong's bell, it is belong to yongle Emperor in MIng dynasty.(But that hangs in the tower now was rebuilt,the older one was destroyed).Yongle Emperor built his rule by bloody war.so he made yongle bells in many tempers all over the china in order to bless the death people .