Just finished a 5160 blade with a whitetail antler handle - thoughts

That slow-cure epoxy trick is the same thing that saved my last antler build. I used a whitetail crown from a buck my uncle took a few years back and kept nudging the bone around until the contour matched my hand. Went with West System for the first time instead of the hardware store stuff and it gave me a full working window, which made all the difference. Drilling antler was the sketchy part for me, so I worked through it slow with a fresh bit and packed the hole with epoxy and some cut-up fibers for grip on the tang. On the steel side, I've done a couple blades out of suspension coil spring and 5160 behaves the same way you described. I couldn't tell you my hardness either since I don't own a tester, but mine holds an edge on cardboard boxes and rope work just fine after a two hour temper at home oven temp. One thing I learned the hard way is to normalize a couple times after forging or heavy grinding, expecially with salvaged spring steel, because I had one warp on me right out of the quench and never got it fully back. The vinegar patina is a good call too. I did mine with mustard smeared on in patches and it came out all mottled, which hides scratches from field work way better than a mirror finish ever did.

Also started normalizing twice before the quench after a couple early spring-steel blades came off the anvil warped and had to be straightened at tempering temps. Slows the process down but I stopped chasing crooked edges. That kindling test out back is the real report card anyway.

Forty years back nobody had slow cure epoxy on the shelf, we peened the tang over a brass washer or poured molten babbit right in the crown and called it done. Held up fine on working knives too. One thing worth passing along on antler handles, the inside of the crown is spongy, so seal that core with thin super glue or wax before you glue up. Otherwise the epoxy wicks into the pith and you end up with a loose grip a year down the road. Learned that the hard way on a moose crown back in the 80s and had to drill it out and reset the whole thing.

Good to see another leaf spring build. I've gotten four knives out of one spring from a dodge pickup, and the trick is flattening it first before you even mark your blades. I clamp it to a flat bar and grind the curve out at 40 grit, saves a ton of time on bevels later. Also for your brother's version, do the handle shaping before final tempering. I cracked a crown once knocking it around on a blade that was allready at full hardness and had to start over.

That hand grinding the bevels part hit home for me. Spent weeks getting lopsided edges on my first couple leaf spring blades til I bolted togehter a little bevel jig out of scrap angle iron and a hinge. Clamped the blade in, ran it across the platens flat, and suddenly my grinds matched on both sides. Took maybe an afternoon to build and it changed everything for me on stock removal.

For your brother's knife, do you drill the tang holes in the crown before or after you fit the guard? I always seem to end up a hair off center once the guard's on and it drives me nuts.