Liam Sneddon and two associates are said to have been arrested in May 2022 after a parcel containing a Glock 17 firearm was discovered.
According to the Daily Record, the 34-year-old was remanded in custody after he pleaded guilty at the High Court in Glasgow to a charge of being involved in serious organised crime.
Sneddon launched a social media appeal three months before his arrest pledging to join the efforts in war-torn Ukraine to help those impacted by the conflict.