It's certainly crimped.
Don't even TRY to use pliers of any sort. It'll simply ovalize the tube and make your life difficult.
What you need is a crimping tool sort of like that used for crimping the rings on PEX pipe or the crimpers used for some electrical connectors like cablevision connectors. But unless you get really lucky on the size and shape of some off the shelf tool you'll need to make your own or have a gunsmith make it for you. Or if you have a friend with some machine tools.
If you're really handy and understand all this you could make your own one time crimping tool using a length of steel flat bar and form the crimping shape in it with careful hand drilling and then split the crimping portion to allow movement with a cut from a hacksaw. But if you're reading this last sentence and thinking "Wha? ? ? ?" then maybe not. How much practice with working on metal do you have?