If the sac is getting twisted - which it shouldn't - then there may be a few causes:
- the j-bar / pressure bar is bent or corroded and catching the sac - examine the bar and replace if it shows either of those issues
- you are using a sac that is either too big or too long - a sac should easily drop into the barrel and the length should have a bit of extra room at the end after you've trimmed it. Using a sac too big in diameter or too long, to try to get more ink, will just end up with problems
- you always need to use talc on the sac, which should aid in the assembly
Hopefully this will help.