I have 158 grain LSWC bullets in .358" diameter. Are they hard enough for good 357 Mag loads? What is considered hard cast? What velocity would you recommend as max before needing Gas Checks?

'hard cast' is anything containing antimony.

15 BHN is about 4 more than I use.

I got nuthin on needing gas checks I have 1 [one] mold that uses them and I generally use it in my 445 super mag.

if I had to guess at a speed I'd say 1400 fps. is about right.
but I've gone to 1650 in my lever rifles, and could probably go past that with H-110.

I shoot them at 1330fps out of a 6 inch 686

Without a problem

With cast bullets “it depends”. Size is probably most important and if you have more than one .357 to feed you may need different sizes for optimal accuracy.

In my experience gas checks help with fudging sizes or high velocity. I normally use half(ish) clip on wheel weights with half(ish) pure(ish) lead, water dropped for everything from mild .38 Special to .358 Winchester loads over 2,400fps.

I couldn’t tell you what the hardness is of my bullets, remember they need to obturate enough to fit the bore and too hard is not a good thing.

13 is hard enough, if sized correctly and lubed. Best way to avoid leading is to coat with Lee Liquid Alox

Or one could powder coat them.

Then you can drive them fast without worrying about leading

Just a bit of info.

I had a 6 cavity Lee needing new hinge pins.
Sent it back, they replaced it with a brand new mold n/c.

I included some bullets I had cast with it.
Asked them to test the hardness: 8-9BH.
They were from recycled range scrap. I figure others did the mixing so I wouldn't need to bother with it.

Many thousands of them thru my 6" K-38. Bore is highly polished. At first they leaded a bit. Just plinkers: 3.5 or 4gr Red Dot. Around 880-900fps.

George

I only asked because I came into 500 of the 15 BHN cast .358 bullets for $10.00 as my friend ordered them in for a guy and then he didn't want them. I had used 12 BHN in the past in my K38, which I gave to my son.