Your sure the oil pump it self is in good working order? Some of the silver glitter stuff can be piston skirt wear, on a new engine, bronze bushing wearing in, flakes from cam bearing installation. At first I was wondering if a cam bearing had spun enough to block the hole. Did you put anti seize on the head bolts or main studs? Some do and it would show up as described. Not sure if you had a new oil pan or used with a baffle. sludge gets caught up under the lip of the hp pans and can let go and plug up some holes. Same with a pick up screen if used. Also if you had used heads, and they were on one way, the oil holes to the top end on the opisite side gets gunked up. Always have to clean that very good. I am just thinking out load so to say. Could have an internal crack as someone said. Lifter is one things, a perfect mic'ed bottom end killing bearings is another all together.