That looks like a 500 gallon Bambi Bucket to me. I would think that a Delta model could pick up a bigger capacity bucket.
Here is a view from the other side of the bucket :
Thats a 2000, yes two thousand, gallon Bambi Bucket underneath a CH-47. We are pulling some serious torque when we pick up 15,000 lbs of water.
Chris Ish, who also has done this with a 250 gallon bucket & a UH-60L.