Hey Cam,
If the sausage is hard on the outside and mushy on the inside, it would indicate some “case hardening”. There is no danger in letting it dry to rock hard, however it may take a long time since the outside has formed a “shell”. My opinion without looking at it is you may be better off throwing it on a pizza and giving the salami another run.
The key factors to normal and even drying when making dry sausage is:
1. Using a large grind plate 8-10 mm (3/8 in or so), you could almost stick a pinky into the whole. Most people don’t have these plates in regular use because they aren’t good for making hamburger or even fresh sausage. However homemade dry sausage is a different breed than any other sausage. The larger particles make the drying faster and more even.
2. Keeping the meat cold/semi-frozen the whole way through grinding, mixing in the cure and stuffing. The meat should come out of the grinder like pellets and that enables even mixing of the cure and spices to coat each particle and keep the particle definition (pretty look on the slice).
3. Preferably using a dedicated stuffer for stuffing. Many grinder stuffer attachments (like Kitchen Aid) will chew up the meat during stuffing, this often raises the temperature of the meat and mashes the particles creating an emulsion (kind of like bologna). As one can imagine, bologna mixture will not create dry salami and will tend to “case harden”.
Most of the success factors in dry sausage happen during the time when the meat is still raw. Hope this is helpful.