POF E2 extraction chamber technology?

[BufordTJustice]

I just got an email from POF regarding a "new" extraction technology; E2 extraction chamber technology.

http://www.pof-usa.com/esquared.html

It appears to me that they fluted the case neck portion of the chamber up to the shoulder of the case. My concern is that this would increase bolt head thrust to unsafe levels. Can some people who are smarter than me opine on this?

Also, I think the concept to seem to be HK derived (basically a partially fluted chamber).

[Eric D.]

I don't think any kind of design 'improvement' like this is ever implemented without some degree of R&D and testing so I don't believe it will necessarily have negative effects but there's always the possibility of unforeseen, higher order consequences. Off the top of my head it doesn't seems like there's enough area exposed to gas on the case shoulder to substantially increase bolt thrust; especially since only the component of force parallel to the bore would add to the total bolt thrust.

But, as the saying goes, if it ain't broke, don't fix it. The system is already designed to ease extraction by not unlocking until after chamber pressure has substantially dropped. The only guns you see with extraction issues due to high chamber pressure are the ones that come overgassed and with trash bcgs.
You also have to wonder how marketing departments twist the technical information. 5X extractor life seems a little lofty. Most of the extractor wear comes from hopping over case rims over and over.

[BufordTJustice]

I agree that it doesn't appear to be immediately defective on its face. However, as you said, it didn't address the main source of extractor spring fatigue.

I wonder if it addressing an issue of the external piston system more so than conditions found on a DI gun?

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[Apricotshot]

Just the latest whizbang doodad from a firearms company.

[markm]

It's POF. Enough said.

That said I'd guess that allowing gas to leak passed would decrease bolt head thrust. Either way... I'll never be in position to find out.

[Leaveammoforme]

I wonder if it addressing an issue of the external piston system more so than conditions found on a DI gun?

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Their demo animation at bottom of screen clearly shows a piston set up. I watched it a couple times laughing at the sound effects.

[spdldr]

This is just old apples in a new basket. Fluted chambers have been around for a long time. For instance, the WW II Tokarev semi-auto rifle used this to make extraction more reliable. More lately, H&K used it to reduce the possibility of tearing the case in half during extraction. The front part of the case "floats" on a cushion of gas, reducing friction and easing extraction.

In my opinion, this is a positive design feature as the 5.56 case is poorly designed for extraction. The rim is too thin for one factor. Thus it should make extraction more reliable. (IMHO one should lightly lube the cartridge cases used in a standard M4 or similar weapon for improved reliability.) This feature of the POF chamber is an improvement, but they should have gone farther and extended the flutes a short distance into the body beyond the neck. It may cause problems with reloading though.

[jbsmwd]

This is just old apples in a new basket. Fluted chambers have been around for a long time. For instance, the WW II Tokarev semi-auto rifle used this to make extraction more reliable. More lately, H&K used it to reduce the possibility of tearing the case in half during extraction. The front part of the case "floats" on a cushion of gas, reducing friction and easing extraction.

In my opinion, this is a positive design feature as the 5.56 case is poorly designed for extraction. The rim is too thin for one factor. Thus it should make extraction more reliable. (IMHO one should lightly lube the cartridge cases used in a standard M4 or similar weapon for improved reliability.) This feature of the POF chamber is an improvement, but they should have gone farther and extended the flutes a short distance into the body beyond the neck. It may cause problems with reloading though.

I really argee. Neck tension and maybe reduce case life/usage.

[Eric D.]

How does a lubed cartridge increase chamber pressure? A lubed cartridge will increase the force (shear stress) on the bolt lugs because of reduced friction between the chamber wall and casing but I don't see how it will increase chamber pressure.

[patrick sweeney]

Theoretically, the film of lube would decrease case expansion, and thus make the combustion chamber just a bit smaller.

However, as a variable effecting bolt lug stress, it would be miniscule compared to the increased thrust due to lack of case adhesion to the chamber wall.