As a professional singer who stutters. Abdominal breathing was not the skill which ended my stutter. It was two elements #1 vocal law. (Breathing, pressurization, and sinus amplification.) #2 language law. (vowels, consonants, and phrases.). The speaking improvement technique was this : #1 Grab-It! : quickly and quietly inhale through an open mouth. #2 Crush-It! : retain captured air in body while speaking, hold breath release slowly as possible. The slower the loss, the longer the phrase. #3 Batch-It! : group 2-6 words and pronounce them as if an unbroken single word. Repeat next batch. I hope that is helpful. A pleasure to expand if needed. :-)