Indybuster,
That thin ring is an integral piece of the bolt head and is of the same chromoly steel. This is not hard but it is tough. It is designed to expand and seal the counterbore and it usually does this very well.
Occasionally the nose of the bolt would fail simply because, in magnum calibers, it is very thin. In a case failure situation, the bolt head might fracture because there was too much clearance between the bolt nose and the counterbore and if the bolt nose was too hard. This sometimes happens because of the thinness of that portion of the bolt head.
There is no question that the use of a Sako extractor compromises the system. This can be compensated for by fitting the barrel with a tighter-fitting counterbore but even then, the Sako extractor can be blown out of the port. Sako blocks this with what many refer to as the "guide rib" but which is, in reality, a block to contain the extractor in the receiver ring in the event of a case failure.
The Howa extractor is a bit better just because it is longer and is pinned in place.
Most of those custom receivers are either made of stainless, in which case they are very soft, or they are made of steel much the same as the Remington in which case they are about the same hardness as the Remington. The exceptions are some actions from overseas (Barnard, RPA) which are quite hard.
The last bolt I made used a Sako extractor and I can live with it but the next one will incorporate a block, like the Sako or the Savage, just for the added safety. GD
