Billa, I am not sure why you are apologizing, as it seems I am the one that offended folks here. I am not at all opposed to wildcatting or cartridge conversion or anything. I am most definitely INTO such things, and INTO handgun hunting (though I have no dislike of rifles). But I just don't see what JDJs bring to the table. I readily admit I may be overlooking something, but to date nobody has brought anything to my attention that I didn't already consider, and such JDJ enthusiasts, I would think, could explain things better than anyone, which is why I even interjected into this thread (cause I ignored it for a while).

I am genuinely interested in reading a substantive, science based "defense" if you want to call it that of JDJ cartridges for HANDGUNS (which in the USA must legally have under a 16" barrel). My opinion of them stands: they offer little over their parent cartridges, are reverse from desirable ballistic qualities for handguns, and are adding even more confusion and obscurity to an already WAY overcrowded and confused reloading landscape. Most people seem to agree with me, because two of my three reloading manuals don't even list the 375 JDJ, the most popular of the JDJs if I am not mistaken. Meanwhile most reloading manuals have 357 Herrett, another Contender wildcat, for example.

How about a comparison?

375 JDJ, 14" Contender, 270 grain Interlock spire point (BC .380) bullet going 2000 FPS (Hornady Manual 8th ed.)
444 Marlin, 15" Contender, 265 grain FTX bullet (BC .275) going 2100 FPS (Hornady Manual 8th ed.)

At 100 yards
375 JDJ will have dropped 0" and delivers a KO of 26.1
444 Marlin will have dropped 0" and delivers a KO of 29.7 (so 444 is better for that charging bear or other dangerous animal)

At 200 yards
375 JDJ will have dropped 9" and delivers a KO of 23.4
444 Marlin will have dropped 9" and delivers a KO of 25.6 (so 444 is better for that 200 yard Elk shot)

At 300 yards
375 JDJ will have dropped 32" and delivers a KO of 21.1
444 Marlin will have dropped 32" and delivers a KO of 22.1 (so here they are almost equivalent).

ONLY AT RANGES BEYOND 300 YARDS DOES 375 JDJ SURPASS ITS PARENT IN BALLISTIC PERFORMANCE. I'd reckon that less that 1% of LARGE GAME are taken by handguns at this distance. 99% of the time 444 Marlin is the better choice.

375 JDJ is a dubious solution to a problem almost nobody has. It is overkill for deer sized animals, and it isn't any better than many long established big bore cartridges, or even its parent, for big/dangerous game.

While the 357 Herrett has merit (which probably explains why it was adopted by T/C and is listed in most load manuals). It delivers extended range performance on deer from a handgun. It improves over its parent. I'm a fan of this former Wildcat!

My 14" Contender propels a 200 grain FTX at 2050 FPS with 34 grains of AA1680.
At 100 yards it drops 0 and delivers a KO of 18.4
At 200 yards it drops 9 and delivers a KO of 16.1
At 300 yards it drops 32 and delivers a KO of 14

It has the same trajectory as 375 JDJ and isn't OVERKILL for deer, which is by FAR the most common large game animal. 357 Herrett is easier to obtain, more pleasant to shoot, cheaper to shoot, and is more than adequate for deer. Nothing is gained from OVERKILL. If the deer dies and is recovered, the job is done. Excess power is NEGATIVE, since it damages meat, exposes you to more noise and recoil, and is more expensive.