I bought a Nova last weekend and then an extended magazine kit for it.
I was able to get 5 shells in the magazine but the 6th slipped part way in and no more. I've heard of other having this problem too. I loosened up the extension tube 3 or 4 half turns. I was able to slip 7 shells in, I then tightened down the extension and cycled the rounds out.
All 7 shells now go into the magazine tube will little effort.