Yep that happens if you attempt to fill a long length and then twist it.
I get round this problem by twisting my sausages as I stuff them. Ie: fill enough skin for 1 sausage, twist away from me. Fill more skin, twist towards me.
This is actualy how it's done commercially as well (saw an amazing machine at atrade show last year. It squirted out eneough meat for one sausage then the whole feed tube rotated, very quickly, then another sausage, rotated - etc. I mean the thing would have been tens of thousands of pounds. But it did it the same way I do - so i must be doing something right lol).
This way not only can you fill your skins to whatever degree you like, but the sausages and skins are tightened up by each successive sausage.
You get complete control over the size of your sausages and the tightness of the skins.
It's pretty much the only way to twist link sausages in collagen skins as well as these have no give whatsoever.
It might seem slow and cumbersome to start with but with a bit of practice you'll be surprised how quick you can turn links out :-)
And it does mean that when you've finished stuffing the skins you don't have to then start fiddling around. It's all done in one operation :-)