Ernie- the reamer that was used was for magazine use.I originally wanted a 6mm remington but he lost his reamer in a fire so I had choice of either 6 cm or .243 win.I already had a lot 6.5 cm brass that I could neck down to 6mm so I went with the creed.Also after looking at load data it seems to me that the 6cm was a better cartridge than the .243 albeit slightly.It has a 26" bartlein 1:7.5 twist and it's running 105 gr. bergers at 3000 fps.I know I'm comparing 105 gr.bullets (536 bc) to 140 grain(600 bc)that are going around 2700 but the 6 cm outperforms the 6.5 out to 1000 yds in my rifles.Btw the bc is just a number they put on the box and when you actually shoot them you find that's what they are-just numbers IMO.