I haven't seen that 3rd Winchester primer Toby mentions in a while I think it's discontinued.
I have no crud ring issues in my Omega with 777. When using this rifle-powder combo, aren't we all supposed to use a weak 209 primer, bore brush,shoot only every 4 minutes or so in warm weather,swab at-least every 2nd shot with alky/windex/washer fluid mix& keep the bore walls oil/lube/solvent-free?????
Oh... I forgot one..... avoid the range with it on high humidity days????