1. You do not quite get the barrel square
2. You square it with a file
3. Since it was not square, barrel is now 17.98 inches
4. As measured by the guys over at the ATF lab.
5. This is Bubba, your new roomate.
6. Ignore the rumor that he killed and ate his last roomy.
7. Well, not ALL of him, anyway.
Seriously, never cut with a pipe cutter- crimps the barrel. Cut with a lathe or power hacksaw. Barrel steel harder than you think. After cutting, needs deburring and recrowning. Did you want front sight on there? Unless you have free access to pretty complete machine shop, and can use the tools, will likely be cheaper to get a second barrel already dolled up.
Give my regards to Bubba.