It was my understanding that the PGU-12B round was an attempt at a +P .38 Special round to increase the effectiveness of the .38 Sp round. I do not know all the ballistic particulars of the round but it was definetely a high pressure round. The first ones I saw was in the late 1970s while I was assigned to AFOSI Headquarters in DC. I was an instructor at the OSI Academy and was the firearms instructor and the Marksmanship Manager for AFOSI. Out issue handgun at the time was the S&W M-36 with a 3" barrel. We found that the PGU-12B ammo was shooting the M-36s loose in very short fashion. We noticed it first on the Academy guns as they were shot much more than the guns in the field. We sent several to the Lackland AFB Marksmanship gunsmiths and they advised that the PGU-12B not be used in the M-36.
That recommendation led to the ultimate adoption of an Officer's sized 1911 built for OSI by the Lackland smiths. Keep shootin'