U inside a shield is RWS, like these 347gr 10.75 calibre bullets. Your 400gr solids should be similar to my 400gr 10.75 bullets shown in the second image, good reinforced nose but relatively thin side walls. I only recovered one of these solids when using my 404 on buffalo and it had fishtailed a bit when caught in the rear hip ball joint of a big bull after penetrating from an slightly angled frontal shot.
The RWS solids don't have any identifying marks as the base is lead with fold over jacket. The 400gr bullets came in RWS round green plastic boxes of 20.