I've got to ask, as I'm not familiar with chamber fluting, what is the reason for doing it? Ease of extraction?
Doesn't it put some funky stresses on the brass when the pressure forces the brass into those grooves or at least reduce the reusable life of the brass?
How about providing another venue for gasses to escape back in to the breech?
Very curious.
Thanks,
-Ron
Random description from the inter web:
"The Vorgrimmler action upon which HK based their roller locked actions predates the AR15 by several decades. The gas piston upper which is the current rage in the AR15 was abandoned by Eugene Stoner for a Direct Impingement principle in his design of the AR15. Almost simultaneously, in the AR18, the gas piston principle was incorporated. That the circle has closed, and the piston become popular again, has been capitalized upon by the folks at HK who have apparently taken the Stoner design and refined it to a point of great reliability. Add a piston and improve the magazine design and now you have a better mousetrap.
The AR Gas piston upper is based on an entirely different operating principle: the venting of gases from the barrel to impinge on a piston which unlocks the action, and causes the weapon to cycle. The Vorgrimmler action is sort of a physics lesson in the subject area of inertia, which instead relies upon a retarded blowback impulse to cycle the action.
The chamber fluting is an accession to the Vorgrimmler action. It is not necessary or even desirable in the Stoner action. Fluting exists in part because there are no primary extraction forces available in the retarded blowback arrangement, whereas in the Stoner action, the initial camming provided by the bolt carrier striking the action pin and rotating the bolt, frees the spent cartridge from its adhesion to the chamber walls as a vital aid to extraction. Due to this primary extraction in the Stoner design the cartridge is already free of the chamber walls before it begins to be extracted from the chamber.
By contrast, in the Vorgrimmler design, the flutes extend down maybe 80% of the chamber walls thus floating 80% of the cartridge casing in an envelope of gas, preventing the case from sticking to the chamber walls, while the remaining 20% of the cartridge is able to obdurate and seal the chamber from additional escaping high pressure gas. The 20% sealing the chamber is easily enough overcome by the extraction forces at work in this design without damage to the casing. Without the fluting, one would experience failures to extract, and torn extractor rims from cartridges, if the Vorgrimmler action cycled at all.
(As an aside, the initial development push by J.T. Thompson and the others at AutoOrdnance used the Blish lock to attempt to achieve the same retarded blowback action for the then standard Government cartridge of 30-06. I have always wondered whether their design would have worked had they tried fluting the chamber in that design.)
To answer your question on how the next round is fed into the chamber, the opening and cycling of the action already having occurred in either action design, the next round is fed into the chamber similarly: the bolt strips the next cartridge from the magazine on its forward journey into battery."
If you don't need those flutes, You Don't want them.!