Not to split hairs, but it is exactly true. There is no way to trace ammunition. You have to show your licensee at the store to show that you are legally authorized to purchase bullets.The store might have a record that you purchased bullets but there is no way to record that you purchased a particular bullet. Unlike hand guns or long guns, bullets do no have serial numbers. There is no way to connect a bullet to the box of bullets that you purchased at the store.Not exactly true. Every time I buy ammunition I have to present my PAL and a record is made of what was purchased. There is no centralised way of tracing but records are there at the store level.
That being said, this is not where they are getting ammunition from. They are getting it from the same source as the illegal guns.
As noted elsewhere in the thread Canadian licensed firearms owners are pretty good at following the law around the privilege of being a firearms owner. The RCMP runs daily police checks on all license holders. Anything that raises flags will initiate at least a phone call if not officers showing up on your doorstep.
Besides there are many gun owners that simply reload and make their own ammunition, it's much cheaper that way. So there is no way to trace ammunition!