Gold standard general-purpose,hunting,self defense,target 158 swc hardcast 850-900fps. Nothing else needed.
One bullet still won't do it all.
A 158 gr bullet won't expand at snub nose .38 Special velocities unless the lead is around 8-10 BHN - even in a cast hollow point design.
Bullets that soft will start to lead the barrel fairly quickly at 4" .38 +P velocities, so you need to step up to a bullet in the 12-15 BHN range for that application.
For .357 Magnum loads where you may be operating at high as 35,000 psi, you need a BHN around 22-24. The downside is that a bullet cast that hard won't expand and might fragment.
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An alloy of 50/50 clip on wheel weights and plumbers lead with 1-2% tin added as needed (in the form of either 50/50 or 90/10 bar solder) for sharp mold fill works well for the 8-10 BHN alloy.
An alloy of clip on wheel weight lead with 1-2% tin added as needed for a good fill in the mould will give you a good alloy with a BHN of 12-15 for general purpose target shooting with loads up to about 20,000 psi (.38 +P).
That same alloy with the bullets cast hot enough to uniformly frost and then quench hardened by dropping them from the mould into a 5 gallon bucket of water with a soft towel in the bottom will give a hardness of 24-28 BHN after about 1-3 weeks of aging. It's a good magnum pressure/velocity target allow good to about 40,000 psi.
That alloy however will often fragment in game at .357 Magnum velocities, so for hunting at .357 Magnum velocity with a cast bullet, I prefer to use 50/50 plumbers lead and antimony with 2% tin added - and then quench harden it (there's still enough antimony in the alloy for it to harden, but it'll take a full 3 weeks). It still won't expand, but it won't lead your barrel significantly during a hunt it is much less likely to fragment, which will ensure good penetration.
The good news here is that you only need two different alloys, one of which is or is not quench hardened depending on the need, giving you three useful bullet hardnesses.
