I recently made a lot of test about sausages, but I am having the same problems with casing splitting on his own when eating it after cooking, the meat does not stick with the casing so it make us feel that the casing is tough . (Collagen Casing)
I changed a lot of brand casing but seems that is not the casing.
1- Add protein to maximize the link between the meat and casing. Fail
2- Drying process and cooking process does not exceed 75 degree. Fail
3- Soften a little when stuffing the meat in the casing. Fail