Originally Posted by Barry

Actually modern tubing is seamless, not seamed tubing. Historical tubing is made from sheet brass and soldered, thus creating a seam. The seam and "bumps" in the bore are just one factor in lipping out-of-tune notes. Bell shape, bore, mouthpiece, venturi, etc. are all factors is how well a natural trumpet plays. I've played and owned several trumpets made with modern seamless tubing that lipped better than some made with "historical" tubing. So it just depends on the individual instrument and maker.