Both the muzzle blast and muzzle flash are accentuated with shorter barrels. I have 243s with barrels from 18.5", a Ruger 77 RSI, to 26", a Remington 700 parts gun, and shoot the 22" Marlin XS7 and 24" Remington 700 CDL-SF parts gun more than any other.
If you're interested in a 20" 243 barrel, I have a matte finished 20" Remington 700 ADL barrel that you can have for $65. This barrel is factory d&t for open sights, but the sights were removed before the rifle came to me.
Jeff
