Oh, I see...
Yes,,, One of those basic automotive 12 or 20 ton H presses would work just fine for doming your buckles. Any kind of home-made domed male and female dies would work good, made from any material. Hard wood or aluminum would work too. I've never tried a pipe cap, but it sounds like it would work great for the top male part of the set.
I use a large wooden dapping block, leather pads and a rubber dead-blow hammer to dome buckles. I've never needed a press.
More tips for making nickel buckles.
I would go with 1/8" thick leather pads rather than rubber pads.
Use dead soft nickel or anneal it before doming. I've had nickel take a half dome, and just spring back up on me.
Get a 4" medium grit cratex wheel for your polisher. When you band saw out your buckle shape, the sides are very rough and takes forever to polish out. Use the cratex on the sides of the buckle blanks, then when you go to the polisher it's not such a terrible chore to polish the sides.
Use some aggressive polishing compound on a tight weave yellow-treated buffing wheel for the first round of polishing. Like bobbing, tripoli or similar.
For the second round of polishing use a normal white muslin buffing wheel with a med or fine polishing compound to shine them up, if you want them shiny.
Most importantly, use all that buffing crap safely. Breathing mask and filtration...etc.
I hope this has been helpful!
-Michael