back when 03A3s were being rechambered to magnums was before the 300 winchester magnum came on the scene

many 06's were opened up to 308 norma

here's the ammo

http://www.selwayarmory.com/hsm-308-norma-180-gr-grand-slam-sp-box-of-20.html

pull the bolt, measure the bolt face

call brownells get the cerro-safe

buy a no-go magnum headspace gauge (works for any belted magnum except 224 weatherby)

if everything checks out, tie it to a tire and fire it

measure all aspects of the case compared to new factory

looks like a bargain magnum