HK and CETME - fluted chamber - case head separations?

[W.E.G.]

HK and CETME - fluted chamber - case head separations?

I've heard it suggested that "commercial" ammo is prone to case head separation failures in HK and CETME chambers.

I've also heard it suggested that reloaded ammo is more likely to separate in HK and CETME chambers.

Anybody have any experience with this?

Its been quite a while since I reloaded any cases that were fired in that type of rifle. I can't recall any separations.

PLEASE TAKE NOTE.

I am NOT talking about case head RUPTURES where the head cracks, and allows the combustion gas to blast back into the the breech - causing what we like to describe as a "kaboom."

I am talking about the situation where there is NO KABOOM. Rather, the brass simply separates roughly mid-way up the case, and the pressure is contained without incident, like this:

This pic shows what I'm talking about.
Forward part of the case, with a "broken shell extractor" still attached.

 

[nalioth]

The roller locked rifles use fluted chambers. Commercial brass has to stretch further than NATO brass (NATO brass has thicker walls)when fired and can weaken a bit more. The extraction process is quite a bit more violent than on other rifles as well, which can lead to the head seperation.


I always advise folks who shoot commercial ammo in their Cetme/G3 rifles to have a broken case extractor with 'em.

 

[AZ Jeff]

Bolt rearward velocity on a roller-locked breech is SEMI-INDEPENDENT of propellant burn rate. Thus, if the propellant in the case is really slow-burning (as could be the case with certain "high performance" commercial .308 ammo, and/or with some handloads), it's possible for the rollers to completely unlock while chamber pressures are still fairly high.

If the pressures are higher than the brass can tolerate, the end result is case head separation. This is aggravated when using reloaded cases, where case wall thickness is reduced to cold-reworking of the brass in resizing.

I never had any separations when I owned/reloaded for my HK-91, but I was careful to use fairly fast propellants, and try to duplicate the M80 ball ammo load as closely as possible.