An operationally ready national serviceman (NSman) was charged in a military court with taking ammunition out of camp and sentenced to detention.
Third Sergeant Jared Mok Shi Jie, 22, is believed to have been found with 10 5.56mm rounds in his bag in September, sources said.
He was court-martialled on Wednesday and given 16 weeks in detention, The Straits Times learnt.
It is unclear how or why he took the bullets out of camp.
Ammunition of this calibre is used for weapons such as the SAR-21, the main rifle carried by soldiers in the Singapore Armed Forces (SAF).
The Ministry of Defence (Mindef) would only say in response to queries that the SAF "regards the theft, loss or unauthorised possession of any ammunition very seriously".
Mindef said the SAF has a rigorous system for the "issuance, use and recovery" of ammunition.
Checks are also conducted on servicemen's personal equipment after training activities, it said.
"In addition, spot checks are conducted during barrack inspections and when servicemen leave camp. Servicemen are also warned of the custodial sentence accompanying such offences," Mindef told The Straits Times.
In 2007, a full-time national serviceman on guard duty went missing with his SAR-21 rifle and several rounds of live ammunition. Dave Teo Ming, then 20, was caught after a 20-hour manhunt and sentenced to nine years and two months' jail, and 18 strokes of the cane.