Spruce,
Thanks for your thoughts on the matter, and let me say right up front that I personally welcome the intellectual exercise of examining different aspects of the evidence. From a hobby perspective, I "like" the 200g loads just as I "like" certain of my guns more than others. . .but I personally had to think thru/read thru/and practice with different loadings & calibers to determine whether I wanted to "adopt" a 200g load for "service." I'm 50 now, and have been reading & enjoying different versions of these discussions ever since I started shooting--I guess I never will get tired of thinking about guns, ammo, etc.! My postings on the 200g loads are just a way of wrestling with this stuff in a more logical way than I otherwise would, and seeing what discussion it may stir up. I've changed loads many times, and may do so again in future!
One reason I've changed loads over time is changing situations: apartment, vs. suburban home, vs. rural home. Also, fairly high threat situation in Houston 1990 vs. a much lower threat now. My current HD situation could feature 20 yd. indoor shots, with upholstered furniture in the way, and is in a rural location with minimal concerns about overpenetration. Thus, I would very likely need to shoot through cover, and would be surprised if I faced a full frontal shot. In a small apartment, I might select Glasers. . . .
With all that being said, I think you hit on some very important points. Here are my thoughts:
1. Yep, an SWC or large meplat FN is what I prefer. All kinds of very convincing evidence indicates that RN configurations don't create anything like full-caliber wound channels, and the same sources convince me that "permanent crush cavity" is the only, or at least the primary, incapacitating agent at pistol vels. (See Fackler; also Beartooth Bullets website.) My own "tests" confirm what I've read about RN slugs tending to deviate in their paths; that could "spoil" a well-directed shot.
2. The reduced weight--higher velocity--improved expansion formula you suggest is indeed the dominant trend in ammo design since about the early 1970s (SuperVel ammo, for instance). There's a ton of evidence showing the effectiveness of that approach, including the superb effectiveness of the .357, as you point out. Believe me, I'm not trying to set myself up against that mass of information & evidence and truly expert knowledge. I would NOT feel poorly-armed with a medium weight expanding slug, as you suggest. Speer Gold Dots in 125g and 135g seem to fit that bill, for instance. The older 158g +P "FBI load" was a similar approach that has proved very effective over time, especially in 3" or longer barrels.
3. With that being said, however, even the premium modern bullets have had trouble expanding reliably at the velocities achievable from snubbies, esp. in .38 SPL, and more especially in standard-pressure loadings. (More about that directly.) Tests in the often-maligned ballistic gelatin show very impressive and reliable expansion, but once they add denim, towels, etc. to the equation they have many instances in which the bullet's HP plugs up with fabric, fails to expand, and then acts as a LRN or LFP would. In standard pressure loads, modern JHPs run 110g or 125g weight, as they won't even try to get expansion from anything heavier. (See Steve's Pages "Terminal Ballistics" data; also
http://www.snubnose.info/tech.htm)
4. As those tests show, along with other sources, it's very difficult to get adequate penetration from that bullet weight in .38 if the slugs DO expand as intended. To me, that is extremely worrisome. Frontal shot at close range with slim bad guy, probably OK. 15 yards away, darkness, through raised arms and sweatsuit "hoodie" fabric, with BG weighing 225 or more, I'm not so confident. That's how bad guys tend to dress in my area, and many are built like that or bigger. Note that Hornady "Critical Defense" ammo is specifically an attempt to ensure penetration. . .so clearly they're aware that's still a problem.
5. Three main reasons I'm more interested in standard pressure loads than I used to be: I really find them easier to shoot well, although I shoot anything adequately; my wife & two kids (both teenage girls) REALLY find +P ammo tougher to handle, and I almost ruined shooting for them by giving them airweights with 129g and 130g +P loads, and even high vel standard pressure 110g and 125g loads, several of which have a surprising amount of flash & intense report (and thus "perceived" recoil). Also, two of my guns are Colts, with minimal use of +Ps encouraged for them, and a third is a Cimarron Lightning (1873 clone).
6. I really hate to use a defense ammo that I can't begin to practice with, and most premium loads are over a dollar per shot. Granted, that's not a "show-stopper" as you can practice with other ammo. . . .
7. My personal primary HD sidearm is actually a .45LC with a couple of Speer 250g GDHP followed by 255g large-meplat LWCs. I'll soon expend the GDs and stick with lead, because my biggest ammo-related concern is using ammo that's been around a while and might have its primer neutralized by oil. My wife uses a .38, and my daughter has downgraded to a .32 due to the misadventures with the airweights (above). .32 load: 115g LFP at 770fps in 2" bbl, shoots thru 6 jugs!
8. Last comment: best answer I have to your thought about 158g has plenty of penetration, is that I don't fundamentally disagree. That's why my wife's load has been a 158g LSWC, although I'll see if she can handle the increased recoil of the 200g :-) Old Brit tests plus newer US military tests seem to indicate that 200g slugs penetrate much straighter, however, and tend to do so even through bone. That doesn't happen with 158g slugs, although LSWC do better than LRN. When you add in my concern about having to penetrate from non-frontal angles, plus shooting thru leather recliners, that's why I want the heavier slug. FBI and Fackler, among others, insist that quick "stops" only happen thru hits in central nervous system; next fastest are rapid blood loss by hitting heart, vena cava, etc., or at least stopping locomotion by breaking pelvis. The 200g LSWC/LFN gives outstanding prospects of achieving those effects if the bullet hits the right place, even though their smaller caliber (i.e. .357 vs. whatever expanded diameter you achieve from an expanding slug) gives you less probablility of clipping veins/arteries, etc., if the expanding bullet performs as designed.
In sum, I trade certainty of penetration & full-caliber wound channel against the possibility of achieving better results if the bullet expands, and thus causes more decisive damage, and also penetrates adequately w/o deviating in an unhelpful way or failing against bone, leather chairs, belt buckles, etc.
Whew, I'll shut up now. Not trying to "beat down dissent," simply trying to give full responses to your thoughtful concerns. Now, if I could get a 200g LSWCHP that could expand at 800fps from a .357 snubbie, I'd be in hog heaven!