I've emailed Speer several times about this bullet. The last time I emailed them they told me that they were about to ship them. That was two months ago. It is a shame. That 170 Hot Cor was my faborite bullet. The delay in the product release makes me wonder if they are ever going to produce that bullet.
I too think it is just another name for a Fusion type bullet, if not the same bullet. After alot of reading, etc, I scrounged up a couple boxes of the Speer 170 Hot Core (they are still out there, but you have to look hard). I shoot them in a 30-30 Ackley, at a decent speed; they are known for deep penetration. I like that in a 30-30, especially for hogs or cow elk/mule deer. One doesn't "need" it, true, but they sure are accurate. They are a "hard" bullet, meaning they don't bump up so fast they are "sticky", so you get good velocity out of the Hot Cors, at least in the 170 30-30. I imagine the Deep Curl will be a good bullet also.
I ordered some Speer Hot Cor 300gr 45-70 bullets awhile back, and the new box they came in said "Plinker" on the side, ha. I called Speer, it's the same old Hot Cor. (Which is what I wanted).
A couple years ago, I had a small buck at 60 yards looking straight at me. I shot him just below the throat with the 170 gr Speer Hot Cor loaded right at 2100 fps, and the bullet passed clean through him, exiting just in front of the hip. He dropped where he stood. Great penetration with that bullet.
A few years ago I bought some "bulk" 170 FN bullets from Midway. As it turned out these were in fact bonded bullets made by the same process as the UNI-CORE series of pistol bullets and had the same dimple on the base. Don't know why Speer let these go but I'm sure they were an early production run in anticipation of going full force into the plated bullet production.
I've tested these into wet saw dust at 85yds. and they performed even better than my favorite 170 R-P Corelokt. near 100% weight retention and excellent expansion. Fortunately I bought a couple of box's of these. If I should ever get the chance to hunt any really big game, or even really large hog's, with a 30-30 you can bet this bullet is what will be up the tube.