Undersized POF Upper

[dexter9659]

Three of my friends picked up 16" POF .556 uppers. At least one of their rifles has suffered several failure to primary ejects. Fortunately for us we had an Air Force armorer on hand to examine the rifle. He ruled out the gas piston and bolt first, and then moved to the ammo and chamber. After firing several different types of ammo (Nato, Nato spec. and .223) we examined the spent casings to find a reoccurring theme... Pressure rings caused by an undersized chamber. I feel horrible for my friend, as he has bought himself a $2,000 mini-14. POF of course wants proof that their upper brings about catastrophic failures. But they have agreed to examine the barrel, casings ect and will cover all shipping costs.

Has anyone else heard of this before?

On a strange side-note: The barrel/muzzle breaks on the rifles are different from one another despite them being "identical" when ordering.

[zemperfi1971]

Most of the times this can be caused by ammo. What type of ammo were you using. If the brass is not resized right you can get failure to ejects. Usually piston rifles eat up all types of ammo but reloads and other low grade ammo eventually kills reliable guns

[jandmtv]

Most of the times this can be caused by ammo. What type of ammo were you using. If the brass is not resized right you can get failure to ejects. Usually piston rifles eat up all types of ammo but reloads and other low grade ammo eventually kills reliable guns

he did say that they tried different types of ammo didnt he?

[RECCE556]

Most of the times this can be caused by ammo POF Uppers.

Corrected...

[QuickOnTheDraw]

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[Addax]

Probably the chamber was not cut to the correct 5.56 spec..

That would be my first guess based on the "Pressure rings caused by an undersized chamber" statement observed by the original poster.

[aplinker]

Most of the times this can be caused by ammo. What type of ammo were you using. If the brass is not resized right you can get failure to ejects. Usually piston rifles eat up all types of ammo but reloads and other low grade ammo eventually kills reliable guns

The piston upper you're running isn't typical. That things runs like a Rolex. I'v e seen POFs go down.

[dexter9659]

I failed to mention the bolt would move about 1/4" back before it got stuck. It took 3 men to eject the stuck casings. All the ammo we put through was all factory new from LC, Fed or Amer. Eagle.