Tony, ,357 v. 300 BLK has actually been a tough dilemma for me based on ease of loading and availability of components and many other factors. Objectively, it would be almost a dead heat with the BLK maybe nudging the .357 out by a fuzz, but it's hard to be that objective about stuff like guns sometimes and I think maybe I might prefer a .357.
A few thing I argue with myself about:
300 BLK:
First of all, the platform is the berries - the size, weight and contoured barrel - perfection of a short, light Handi and ready made.
There are no "forming dies" for this one - just a cheap set of LEE dies and yer off and runnin'. I modified a 7.62x39 LEE collet dies easily to neck size only. I've done a considerable amount of case forming and this one is cake.
Yes, chopping brass can be a pain, but if you're spending for a $1k can, what's $40 for a Harbor Freight Mni-Cutoff saw? That said, I use the table saw and dodge the offcuts.
Uses almost exactly the same amount of lead and powder as the .357.
Has the fast twist desired for the long, slow bullets but works well with short, fast bullets.
30 cal is easy to cast for and mould designs abound
Has slightly better sectional densities per same bullet weight as common .357 projectiles - should shoot flatter, should have better penetration for like weights.
Supersonic loads are useful over a wide range of bullet weights, say 110 grain to 220 grain and then those honkin' 250s.
Very common brass.
Can use the same primers if you already use small rifle in your .357.
357 Mag:
First of all, if the .357 were available in this platform, I never would have discovered the 300 BLK.
Pretty simple loading, no lube, no mess,.... no chopping.
Uses almost exactly the same amount of lead and powder as the .300 BLK.
357 cal is easy to cast for and mould designs abound
Has slightly less sectional densities per same bullet weight as common .308 projectiles - should shoot slightly less flat, should have slightly less penetration for like weights BUT makes a bigger hole with non-expanding bullets - which is not unusual for subs.
Supersonic loads are useful over a wide range of bullet weights, say 110 grain to 220 grain and then those honkin' 250s.
Very common brass.
Can use the same primers if you already use small rifle in your .300 BLK.
There are other things to consider but the 300 BLK Handi pushed me over the edge. I keep trying to think of how the .357 would trump it soundly considering my wants and needs but I'm not finding it. Oddly, I have never been a big fan of the .357 until I shot it in a carbine, but, then I have no desire to be associated with the tacti-cool mall-ninja persona either. Two cartridges I have never cared much for seem to have both fond a way into my battery and now are duking it out for "who's better."