I bought a hydraulic forming die in 6MM Dasher, from the classifieds on this site. I'm not going to lie, the reason I purchased it was because I was curious/intrigued :
First thing that I 'd like to point out, is that they really are not that messy. You can seriously reduce the mess with some simple pointers:
1) fill the cases with a syringe of some sort (like this: http://www.petco.com/assets/product_images/8/800443070970C.jpg)
2) ALWAYS pull the 'cylinder' out of the die, before lowering the press ram (removing the case from the die)
3) Have a large pan or bucket to shake the water out of the cases after your done forming
I had ZERO water outside of the case by using the 3 tips above. (With one exception, explained below)
The second thing I'd like to point out is that you MUST have new brass, or freshly annealed brass.
In the pictures I have below, the 'smiley case' shows a split neck. For that case, on the third swing of the mallet the piston slammed down into the die and bottomed out. (It won't hurt the die if that happens). The water shot out of the split in the neck, immediately relieving the hydraulic pressure in the case. This case had 5 firings on it in my 6BR without being annealed. This is the case that turned the process into a watery mess
(NOTE - I was kind of expecting this, knowing that the brass was already work-hardened, so it wasn't a surprise.)
Lastly, it helps to use a consistent yet aggressive swing with the mallet. I did a little test to show what's happening to the case with each swing. See the pics below (The numbers on the cases refer to the number of swings with the mallet. The last case, with the 'x' on it, I actually hit it 10 times. The extra effort made no difference; anything beyond 5 swings is likely a waste of time!)
And finally, I feel the end results are pretty awesome, considering I used no primers, powder, bullets, or barrel life, and didn't have to create false shoulders. The end results of case IV and V in the above pictures are VERY close to my 3x fired Dasher cases. After using this process you can load and shoot with full dasher loads, which I feel is another benefit, because your first firing does not have to be a reduced load. This process goes pretty quick too! I could see knocking out 50 cases in 30 minutes easily (minus dry time).
If you can't tell, I was bored this evening, so I typed a up a review
Hopefully someone can gain some knowledge from it,
Walt

First thing that I 'd like to point out, is that they really are not that messy. You can seriously reduce the mess with some simple pointers:
1) fill the cases with a syringe of some sort (like this: http://www.petco.com/assets/product_images/8/800443070970C.jpg)
2) ALWAYS pull the 'cylinder' out of the die, before lowering the press ram (removing the case from the die)
3) Have a large pan or bucket to shake the water out of the cases after your done forming
I had ZERO water outside of the case by using the 3 tips above. (With one exception, explained below)

The second thing I'd like to point out is that you MUST have new brass, or freshly annealed brass.
In the pictures I have below, the 'smiley case' shows a split neck. For that case, on the third swing of the mallet the piston slammed down into the die and bottomed out. (It won't hurt the die if that happens). The water shot out of the split in the neck, immediately relieving the hydraulic pressure in the case. This case had 5 firings on it in my 6BR without being annealed. This is the case that turned the process into a watery mess

(NOTE - I was kind of expecting this, knowing that the brass was already work-hardened, so it wasn't a surprise.)
Lastly, it helps to use a consistent yet aggressive swing with the mallet. I did a little test to show what's happening to the case with each swing. See the pics below (The numbers on the cases refer to the number of swings with the mallet. The last case, with the 'x' on it, I actually hit it 10 times. The extra effort made no difference; anything beyond 5 swings is likely a waste of time!)


And finally, I feel the end results are pretty awesome, considering I used no primers, powder, bullets, or barrel life, and didn't have to create false shoulders. The end results of case IV and V in the above pictures are VERY close to my 3x fired Dasher cases. After using this process you can load and shoot with full dasher loads, which I feel is another benefit, because your first firing does not have to be a reduced load. This process goes pretty quick too! I could see knocking out 50 cases in 30 minutes easily (minus dry time).
If you can't tell, I was bored this evening, so I typed a up a review

Hopefully someone can gain some knowledge from it,
Walt