[removing seam]

Im building an Sa2 missile from trumpeter and the rocket comes in two halves. How should I approach removing the seam between the two parts? Im not really a fan of putty/fillers and know you can use plastic cement for this but I wanted to ask around before I attempt it. 

[rocket seam lines]

Im building a trumpeter sa2 missile and the rocket comes in two halves. I used melted sprue and plastic cement to fill the gap and it worked pretty well. But what grades of sandpaper should I use on the seam line to smooth it out? I used 400,600,800,1000,1200,1500 in that order but are there specific grades that should be used ? or just keep going finer and finer to remove scratches?