I've got an action to use for my first custom rifle. The donor is a Rem 700 BDL, currently chambered in .270 win. Will this action work for a .300 RUM, or do I need to stay with a non-magnum cartridge? How do you decide on your barrel length? This rifle will be built strictly for shooting whitetails out to 600 yards. Usually from sandbags on a bench, occasionally from prone using bipods or a backpack to rest on. I'm not at all concerned about weight or overall length, a 25 lb rifle with a 36" barrel would be fine if it shoots tight groups. I was hoping to shoot either 190 or 210 gr VLD's, which require different twist rates according to Berger's website. 1/12" and 1/11" respectively. Which twist rate would allow for a little flexibility in bullet weight?