PDI Outer Barrel Scraping in Well/Warrior L96

[SoupOnHerHed]

I've got a PDI Fluted Outer barrel for my Well/Warrior L96. When I got it, it was about 2mm too long to screw into the bolt housing and have the mag release and hop unit aligned properly, so I had to cut 2mm off the end.
When I put it in and put the gun together, I realised the cylinder would scrape on the outer barrel. At first, I thought this was due to bad sanding down of the cut part, so I sanded it down and now it's smoother than the stock barrel (which doesn't scrape).
It still scrapes when I push the bolt forward. I found that if I put 10cm strips of electrical tape down the inside of the barrel it prevents the scraping, but after about 10 cycles, the cylinder catches the tape, which then rolls and up and causes it to jam.
The inside of the PDI barrel is completely smooth up to about 6 or 7cm down the barrel, then it appears to be rifled and slightly bumpy, not sure why though. I have a feeling this is what causes it, as apart from that, I can't tell any difference between the stock barrel and the PDI one.
I have tried three different cylinders; the stock one, the steel one from ASPUK and a LayLax Teflon coated one.

Any suggestions on how I can stop this scraping?

Thanks.