Let me firstly say thanks for your reply, and I'm sorry the article didn't raise the discussion in the professional or academic circles you were hoping for. The overarching argument seemed to me to be a good one, although I agree with the caveat above that the military will simply plug all weight gaps with other equipment as and when they come available. If you could ensure the made-up weight consisted of the sort of kit you talk about (MP7s and P90s notwithstanding for a moment) then it seems a perfectly sensible approach to current conflicts. Of course, what goes on in the future is a different matter. But if a greater degree of flexibility comes out of suggestions like yours, that can only be a good thing.

On to the terminal ballistics. Hoplophile is a new one on me, and a good one too, but unfair in this case I think. "DocGKR" is Gary Roberts, a recognised wound ballistics expert. Dr Martin Fackler (who I think you must have heard of) is also down on these rounds. Neither, as far as I can tell, qualifies as a gun nut, cultural bias aside.

Both men point to a very small permanent wound channel and little to no secondary effect, which to me (and I stress I am not an expert by any means) makes a lot of sense. The only reliable way to cause incapacitating wounds aside from shot placement is to use weapons and ammunition that create large permanent wounds that, to put it bluntly, will bleed a lot.

Ironically enough, at 4-500m, this would be less of an issue. Any 10"+ perforating gunshot wound is going to cause a fighter enough difficulty at that range to put them out of the fight. But at the <300m range you're talking about, rapid incapacitation becomes pretty crucial as I see it, and not just from anecdotes that may relate to unusually resilient individuals (such stories can be rustled up for just about any calibre).

If you acknowledge the utility of gel tests, I wonder how you square the following with what you've seen, and would ask how the test methodology and results compare (assuming you have access to the articles cited)?

(Edited quote from the lightfighter link - I'd urge you to read the whole thing in situ)
Quote Originally Posted by Dr Gary Roberts
Other than being able to perforate soft body armor, the 5.7 x 28 mm used in the FN P90, as well as the 4.6 x 30 mm fired from the HK MP7 cause wounds less incapacitating than those made by 9 mm FMJ fired from a pistol...

Several papers have described the incredibly poor terminal performance of projectiles fired by the FN P90.
--Dahlstrom D, Powley K, and Gordon C: “Wound Profile of the FN Cartridge (SS 190) Fired from the FN P90 Submachine Gun". Wound Ballistic Review. 4(3):21-26; Spring 2000.
--Fackler M: "Errors & Omissions", Wound Ballistic Review. 1(1):46; Winter 1991.
--Fackler M: "More on the Bizarre Fabrique National P-90", Wound Ballistic Review. 3(1):44-45; 1997.
--FBI Academy Firearms Training Unit. FBI Handgun Ammunition Tests 1989-1995. Quantico, U.S. Department of Justice--Federal Bureau of Investigation.
--Hayes C: “Personal Defense Weapons—Answer in Search of a Question”, Wound Ballistic Review. 5(1):30-36; Spring 2001.
--Roberts G: “Preliminary Evaluation of the Terminal Performance of the 5.7 x 28 mm 23 Grain FMJ Bullet Fired by the New FN P-90 , Using 10% Ordnance Gelatin as a Tissue Simulant”, AFTE Journal. 30(2):326-329, Spring 1998.
--Roberts G: “Terminal Performance of the 5.7 x 28 mm 31 Grain SS-190 FMJ Bullet Fired by the FN P-90 in 10% Ordnance Gelatin.”, AFTE Journal. In Press.

It is all basic physics and physiology. Look at the surface areas in contact with tissue for 9 mm FMJ and JHP compared to 5.7 mm. When both are point forward, the 9 mm FMJ crushes more tissue than the 5.7 mm; for the short time that the 5.7 mm is at FULL yaw, it crushes a bit more tissue than the 9 mm FMJ. At no time does the 5.7 mm crush more tissue than the expanded 9 mm JHP--even when the 5.7 mm FMJ is at full yaw, an expanded 9 mm JHP crushes more tissue. The relatively small temporary cavities produced by both the 9 mm and 5.7 mm projectiles are not likely to cause significant injury to the majority of elastic structures of the body. As with any penetrating projectile, if either a 9 mm or 5.7 mm bullet is ideally placed to cause significant damage to the CNS or major cardiovascular organs, a fatal result is likely.