How to keep sausage cases from splitting?

I make the sausage mix and put it in the casing. Although, when I twist them to make them into individual sausages it splits and I have wasted the casing and sausage meat.

The sausages split literally as I twist them. I use ‘Single dry beef collagen casing 28mm’ cases. I store them in a dark safe cupboard where they cannot get damaged. Before filling them I wash the to make sure they are no snags

Any help would be appreciated,
Domford