Hi Incursion;
The P7PT8 was a P7M8 look-alike, made by H&K specifically & only for training. It was furnished either with a light blue colored slide or a typical blackened slide with an indented light blue "dot" on the right side of the slide, at the front, so that the user couldn't easily mistake it for a "real" P7M8. It fired a special reduced-power training round, designated the 9mmx19PT, with a plastic bullet (auf Deutsch, PT meint Plastik-Training, nicht wahr?), which developed a muzzle energy of only 210 Joule, but at a speed of 1000 m/sec, vs. a typical 9x19mm round, which would have average numbers of 490 Joule and 350 m/sec, from a P7M8. The external dimensions of the P7PT8 were essentially identical to the P7M8, but the fully-loaded P7PT8 weighed only 806 grams, vs. the loaded P7M8 at 950 grams. Obviously, the internals were rather different, though the "feel" or "handling" (Handhabung) was supposed to be identical between the two guns.
(The "combination-caliber" gun noted by another poster above was the P7K3, which was capable of conversion between 9mm Kurz [that is, .380ACP], .32ACP, and .22LR.) Best.
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"Potius sero quam nunquam."