Sometimes he just chews on them and spits them out.What type of snails do you feed your porcupine puffer? I tried once to get mine a few however it was way too hard for my puffer to break its shell. No matter how hard he tried. My porcupine is about 5 inches too. I forget the species of snail since it's not the most common type.
The nassarius snails are his favorite. He blows them out if the sand. He also eats small nerite snails, hermit crabs, Florida ceriths, (usually in cerith shells).