I love Unique. Kinda hard for me to believe sometimes, but I probably use more Unique and 231 than any other powders anymore. Even more than 2400 and H-110 these days.

In Handloader #217 Brian Pearce has a bunch of loads listed for both standard and plus P levels. I have used several of them in my guns.

He shows a load of 5 grains of Unique under the 173 grain Lyman 358429 Keith bullet as being pressure tested to be at, or under standard SAAMI pressure levels of 17,000 psi, and giving a muzzle velocity of 932 fps.

In my 15-3 it is a nice and accurate load, and for defense, I would have total confidence in it, especially if I had to go through winter type clothing.

Since you are asking about loads for a 158 grain cast bullet though, he shows 4.8 grains of it under the Speer 158 swaged swc hp as giving 898 fps from a M-14 S&W. It is a lighter charge weight load than the one for the heavier Lyman bullet because the Speer bullet is soft and will lead at speeds much over 800-900 fps, so he was staying within those guidelines.

In the +P load data he shows 5.5 grains of Unique under the Lyman Keith bullet as giving 1002 fps from a 6" M 14 S&W. I have fired this one too, and it is as accurate as the standard pressure load, and it is definately one to be taken seriously for defense if your gun will handle them.

It would be a safe load with any 158 grain cast SWC that has an as seated depth inside the case that is no greater than the Lyman bullet, since the Lyman bullet is heavier and has as long, or even longer bearing surface. I have had no trouble what so ever when switching from the 173 Keith bullet to 158 cast swc's. Recoil is a bit less with the lighter bullet, and accuracy remains about equal with the slugs I have on hand.

As always: Start low and work up in your gun watching for any signs of excess pressure.