Getting a metal airsoft gun in canada (too low a velocity is illegal?)

Alright so I made some money recently, I wanted to order the sword cutlass gun frome ast coast airsoft (a replica from the anime black lagoon), however I was informed that they can’t guarantee that it will make it across because of all things, it fires too slowly.

What gives? How does a gun firing too slowly make it a problem.

Anyways, this is the only place you can get this gun still, so I was wondering, with the gun beint $150 and $25 shipping, is it worth the risk? I really want one of these (ideally 2), what are the chances of it being picked up at the border? Is there perhaps a time of year when they would be less attentive and just try tog et stuff through quickly?