Shipment refresh is playing against the house. The first refresh is terrible to begin with. By the third refresh, you're playing a crooked game of loaded dice in a dark alley, just for the action, and you don't even care.
If it's worth the cost of X number of refreshes to you, decide on that number and stick to it, every 6 hours. And congrats for being able to smile while pissing money away into the interwebz like that. You must have it good, my friend.
From my own experience, I would put chance of a raid gear showing up on a refresh to be no more than 5%, at best. That is probably very generous. If it IS in fact 5%, this means if you refresh 14 times, you still have only a 50:50 chance of getting a raid gear by the end.
To secure about > 95% chance of getting a raid gear, you would need to bank on about 60 refreshes.
Of course this can just go on and on and on forever.
Using the 5% figure, if you simply check shipments 3x a day for free, the chances are about 88% that you will discover at least one raid gear in each 2 week period.
