I have had experience with both pistol caliber carbines and shoulder stocked pistols. FWIW, I agree with 355Sigfan. They are neither fish nor fowl and not good at being either.
Further, if you are a military officer issued a pistol, you would have to carry the pistol in the issue holster, and where do you carry the rest of the "carbine"?
Contrary to common belief, troops don't just carry any old weapon they might think they like, and "unofficial" stuff can get one in trouble in a lot of ways.
Jim