If you are putting too much downward pressure while trimming that can cause a ridge to form on the brass. I have been using the same setup for all my rifle calibers for years, and have gotten an occasional bur when I exerted too much downward pressure. Another possibility is that the blades that deburr are not dropping down enough. I keep a piece of 2x4 on the bench to give the cutter assembly an occasional few quick downward taps to clear it of brass particles/dust which may be a source of binding the cutter blades interfering with them dropping down into their proper position. The Lee haters are ever quick to be dismissive of Lee products. When Lee uses non-metallic products it's "cheap plastic", but when other brands use it it's a "high tech polymer"
. I have been reloading for 30+ years with equipment from the major brands [except Big Blue where I could not justify the expense for MY needs] and find Lee products satisfactory and have been giving me good service all that time.