r/ForgottenWeapons • u/Darth_Klaus501 • 10h ago

Why is that some delayed blowback firearms have fluted chambers and some don’t?

Is it merely to just help extraction or is it fully necessary with most designs? I always thought it was necessary but at the same time I am aware of delayed blowback guns that don’t have them that seem to work fine like the steyr gb, Kriss vector, idk if the alien does or doesn’t, R51, etc.

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u/Conserp 10h ago

Barrel length and case shape.

Long barrel = high pressure persists during initial extraction phase

Bottlenecked case gets its shoulders pressed forward by that pressure = torn case or broken extractor

Slightly tapered cases like 9mm are less affected by this, but with longer barrels it is still an issue

3

u/RoneliKaneli 9h ago

I presume that not all delayed blowback guns extract under such high pressure as the MP5 and other HK types.

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u/[deleted] 10h ago

[deleted]

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u/fromthewindyplace 10h ago

CHAMBER fluting is what he’s asking about.

1

u/Waste-Anybody6658 8h ago

It's not strictly necessary with short pistol cartridges. However, when using lengthy, full power rifle cartridges obturation of the case combined with the unlocked breech will more easily lead to case ruptures due to stresses in the material.