You don't need high brass hulls to load field loads. High brass hulls are used to designate hotter and heavier loadings but it is what is inside of the hull that matters.
You can use a Federal Gold Medal, Remington STS or Winchester AA hull as your hull. Go to the Alliant web site and look under 12 gauge and any of the above mentioned hulls. You will find loads using easily available wads ranging from 1 oz. to over 1 1/4 oz.
As there is more room in a Federal Gold Medal straight walled plastic hull than many other tapered hulls, you can probably load a little heavier shot charge with a Federal hull if that is your goal.
A Remington STS hull, 25-27 grains of Alliant Herco, 1 1/4 oz of your favorite shot, a Remington SP12 wad and a Remington 209P primer makes a dandy heavy field load. Velocity is around 1250 fps and recoil is manageable.
Be sure to consult a loading manual and weigh your powder and shot charges.
The same suppliers for my target components have almost everything I would want for field loads. I would use the same hulls as I would for target loads. The Federal GM hulls are a great choice for the reasons Ed mentioned above. High or low brass (steel) should not make a difference in modern loads.
Use different hulls to designate a certain load so you know what you are putting in the gun for each hunting trip . I usually loaded #4`s in a black hull , #5`s in a green hull and #6`s in a Red hull - all different from my trap loaded hulls so they weren`t confused plus I would mark the boxes in accordance with the shells . There are plenty of excess hulls at any range , just use the proper components for each hull .
You never mentioned what type of "field" loads you are looking for. Be more specific and you will get more pertinent responses. My favorite "field" load is 28gr Longshot under a Versalite wad pushing 1&1/4oz of #7. Vaporizes anything hit! AndyH