Search:

Are those collagen skins ?

half a cup of bread crumbs is a lot per kg, I don't add any bread crumbs. They will absorb a lot of moisture and probably account for the soft/spongy texture

certain binding agents can give them a spongy texture, what if any binder are you using ?

super market sausages are just floor scrapings, lips and assholes ground up and stuffed in a collagen tube. dog food at best. Cant beat home made sausages.