That's an interesting attitude!!!And I don't understand your headspacing.I was taught to slightly counter sink my primers.So how much headspace will I have? [huntert243sgk]
You're confusing two issues here. You're quite right in saying primers should be seated so that their faces are below that of the case-head. This is to (1) avoid a slamfire as the bolt is closed, and (2) to place the primer cup and the internal anvil's feet onto the floor of the case pocket, under slight tension ideally, to ensure that all of the firing pin's energy is directed to crushing the explosive pellet between the dented cup and the anvil point.
The headspace issue is that of setting the case-shoulder correctly in relation to the chamber. If the shoulder is pushed back too much in sizing, an excess headspace condition is created. When the firing pin falls, it pushes the entire cartridge forward until the front of the chamber stops the movement. As the primer simultaneously ignites, Newton's third law will see it attempt to move backwards out of the case, and it does so until it hits the bolt-face. So it backs out of the case-head a little, the exact amount depending on the headspace. At that point there is a gap between the bolt-face and the case-head as shown in bigedp51's animations - if the headspace is optimal there will be only one or two thou' clearance, but potentially much more of there is excess headspace. The front of the case walls now freeze (obturate) against the chamber walls as the charge burns and internal pressure rapidly increases, and the case stretches at the rear end just ahead of the solid web until the case-head hits the bolt-face and is stopped thereby. This stretching produces case-separation if signicant enough after a few firing / sizing cycles.
As the case stretches backwards, it reseats the primer in the pocket. A very flat primer face is usually taken as a sign of excessively high pressures, but it can be caused by modest or normal pressures when the headspace is excessive as its rear end is unsupported whilst sitting proud of the case-head allowing the face to flatten out against the bolt. A very (too) light load can produce a fired case with the primer sitting proud of the case-head as the case is pushed hard enough forwards into the chamber by the firing pin blow to push the shoulders back and temporarily create excess headspace, the primer backs out and the case doesn't stretch back to reseat the primer, this process being repeated over multiple firings and hence the advice not to use cases that have been fired with very low pressure loads to be then loaded up to full-house pressures.
So far as the OP's question goes, I'd agree that the Fed 215 is one of the 'hottest' primers on the market, so any other magnum primer can be safely substituted. The standard Winchester WLR is almost as hot and can used in lieu too.
Magnum primers don't always produce larger flames. Some models achieve their ends by incorporating powdered glass or metal which is forced into the main charge as incandescent particles helping large charges to ignite.
So far as cups are concerned, SR primers see different brass thickness between standard and magnum / BR versions, but all LR primers use 0.028" thick cups irrespective of their designation / role, so that's not an issue here. Some makes have a reputation for being 'harder' or 'softer' though as evidenced through flattening under pressure, and whilst probably exaggerated by shooters, this likely happens through minor differences in the brass alloy used to make them.
)... which ever fits your style of shooting.
