The Underwood Xtreme Defender bullet is a new-technology non-expanding approach that uses outwardly curved channels to create hydraulic slicing that reaches further, in terms of permanent wound channel size, than any expanding hollow point technology bullets. The Xtreme Defender is a lower mass variant of its Xtreme Penetrator predecessor, in interest of velocity (and thus muzzle energy) maximization with penetration preservation.
Its rated velocity, 1550 fps, corresponds to full-size pistol testing, and its penetration, rated at 16 inches, is also lowered by short barrel pressure limitation, so is likely right in your 12-15" favored range with which I fully agree.
The RAMI's slide mass, aluminum frame, and low bore center combine to produce industry-enviably low recoil, and the DPM Systems Technologies springs have as well established themselves as effective in minimizing recoil, something that I've begun to believe is predominantly a result of slide bottom out intensity (watching slow motion YouTubes at 0.25X speed).
And in terms of bullet manufacturer quality, I have a Frankford impact hammer that enables nondestructive bullet disassembly. My experience thus far has shown Underwood to have by far the most intense and consistent disassembly forces, and powder fill depths have been imperceptible, bullet-to-bullet, a huge contrast to the other brands I've so far encountered. I trust Kevin Underwood's quality above all others, period.
So again, in sum, my happy situation is 15 rounds, completely concealed, with industry-best performance (with minimal short barrel penalty) and no additional risk of frame damage. The only downside is you can no longer impress the ladies with how easily it racks. Once they feel the buttery smooth trigger, however, it's game over.
Truncated bullets, and "hydraulic slice" sound good, but before altering a gun to operate with them, especially if running in pressures for which there are no SAAMI standards:
How will they actually perform in real life? Sectional density, or lack thereof in the target medium plays a large role in how a bullet will perform. For comparisons:
• Sectional density of Lung tissue is approximately 0.24gram/cm3
• Sectional density of Ballistics gelatin, and muscle tissue is approximately 1.06 gram/cm3 which is 4.5x denser than lungs.
From use in hunting I have seen the difference of how a "self defense" round actually performs in use as compared to ballistic test videos. At 10 feet, in ballistics gelatin, with sectional density of 1.06gram/cm3 tests show full expansion of the round at 1" to 1.5" of depth, and permanent wound cavity of about 1.5-2 inches. Depth of penetration 10-12 inches.
The same round in hunting situation expands at 4-6 inch of depth, almost 5x times deeper than it expands in ballistics gelatin. Even at 50 yards it passes completely through a deer which is 14-16 inches on a slight quartering away shot.
An average size deer has about 1/2 inch of muscle tissue (sectional density of 1.06gram/cm3) to penetrate before it enters the "void" of the lungs which has a sectional density of .24gram/cm3 (almost 1/4 that of muscle or ballistics gelatin).
I came to the conclusion those differences are the result of the voids, and resulting lower sectional densities a bullet actually encounters.
While the design of truncated rounds shows good results in gelatin, and good barrier penetration, I have to question where such a bullet would meet enough sectional density enabling it to perform the "hydraulic slicing" needed to do more than act like an expensive FMJ?
The only thing I can think of with a sectional density close to lung tissue would be a semi-damp foam sponge, and if someone could show good performance with foam sponge sandwiched between some pork ribs I'd buy some of the truncated standard pressure rounds.
For myself I’d be cautious of anything for which there’s no SAAMI standards.
