In practice, the FBP proved a reliable weapon and well developed for the rigors of military service. Its steel pressing manufacture approach made the weapon suitable for mass production. If there proved one downfall it was in accuracy at range - which can be expected of a "mutt" gun design like the FBP. The original full-automatic-only m/948 was then followed by the improved m/963 which introduced a select-fire capability by incorporating a semi-automatic action. The m/963 was then, itself, followed by the modernized m/973 which introduced a perforated barrel jacket to help with cooling. These were not produced serially. Internally, however, all models of the FBP line remained largely the same.
The Portuguese Army eventually gave up their FBP submachine guns in favor of the Israeli UZI. FBP service therefore spanned from 1948 into the 1980s. The weapon also fell into use by non-military elements in combat across several former Portuguese colonies.
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