On my Atlas 618 they are .202 - .203 in diam. and have a 27.5 degree nose angle. They are made of steel for a reason, brass is for decoration.
Also it is important to round over the long end of the angle.
I was just about to write the same thing. Brass is too soft. You didn't say which lathe you have. The compound swivel lock pins for the 6" are M6-309. For the later 10" and all 12" they are 10-309. In Downloads is a drawing of the 10-309 that I made from one of mine about six years ago. I haven't checked recently but last time that I did, they were still available from Clausing, so they won't release the Atlas drawings.
Note that on mine, I measured the angle of the bevel as 60 degrees (or 30 degrees for the included angle. And the diameter is 0.310". Note also on the sketch the radius cut on the bottom of the bevel.
I have a 10 and was going to do some milling with the attachment and the pins would not slide back to remove the compound so I drilled the pin and used a screw to remove them, I made a couple out of brass for now and cut them at 30 degrees until I make a couple out of steel. How do I access downloads?
BTW, if you drive a groove pin into the hole in the compound swivel locking pins, and then grind it off flush, you can still use the originals once you have confirmed that they will now slide freely all of the way through the holes in the Swivel.