I am building a light weight custom 338 calibre long range rifle and am deciding between the 338/378 Wby or 338 Lapua. The barrel is a 30" Benchmark ABS Carbon Fibre wrapped and will be throated for a 300 grain projectile either SMK or Berger. Seekins magazine and bottom metal will complement the Defiance repeater action housed in Manners light weight carbon fibre stock. Now I am sure this debate has already been through the forums before and wanting to take a somewhat short cut I am open to all suggestings, criticisms, for and againsts for each of the two cartridges above. I have seen where Kirby Allen has done a lot of work using the Lapua cartridge. I would like an honest opinion as to why the Lapua is perhaps the better option obviously being a non belted cartridge might be the primary reason for selecting this round. I am aware Lapua brass is top quality stuff in comparison to Norma brass and the 338 Lapua has a better selection of reloading dies with bushings whereas there are no such dies with bushings available for the 338/378. With that aside can someone offer other plausible opinions please bearing in mind that I already have a Weatherby Accumark in 338/378 with its standard Krieger barrel that will group 1/2MOA however it weighs 10 pounds 4 ounces with a 2.5-25x42 March scope, however I want to go lighter to use this rifle as a walk in and stalk rifle as well as having long range capability. I have several hundred cases in 338/378 and top quality Redding reloading dies and need to be really convinced to move away from this cartridge in favour of the 338 Lapua.