I bought some of those 300gr for my 338/06 but haven’t loaded any up, was for a self guided African hunt but ended up using my 9.3x62.
We were using Winchester 338Win factory loaded 300gr cartridges on the Buffalo for the meat works in the old days, we had to head/brain shoot them but it worked well on chest shots to if it came to that.
Yes those Bertram slugs are cheap, I bought a heap of .416 & 480gr .458 bullets for load development & shooting practice, I’d not trust them on DG !!