I was at a local rifle match a few weeks back, and I noticed that a fellow AR shooter had removed the flash hider from his AR (a Bushy IIRC).  He was shooting with just the bare threaded bbl.  When I asked him why, he stated that the flash hider would shift his POI drastically  (4-6" @ 100 yrds. again IIRC).  This was a new one on me, and I was ready to call B*lls*it, but the guy was a very skilled shooter.  He cleared every stage, and ended up taking first place.

I was just curious if there was any truth to this, or is this guy a crack head (albeit a good shot).

Yes muzzle devices can shift your POI from a bare muzzle.

That is why you zero with your muzzle device on.

Muzzle devices can also effect your group size (for good or ill).  Generally the bare muzzles with a target crown are the most consistant.

how would a device which removes turbulent gas from the muzzle be a liability?

Quoted: how would a device which removes turbulent gas from the muzzle be a liability?

It could remove gas unevenly.

I have a heavy barrel A2 style 16 inch upper (not a bull barrel or target barrel but heavy even under the hand guards like a HBAR).  When shooting good factory ammo it will shoot one ragged hole at 100 yards with a scope mounted.  It has an A2 birdcage flash hider attached.  I never have tried the barrel without the flash hider.  The reason I tried this was because I was having trouble getting 1 inch groups with mil-surplus ammo.  I bought some $16 per box (20) Winchester Silver Plastic Tip ammo and tested from sandbags.  I was quite surprised.

Does anyone make a flash suppressor that doesn't effect accuracy, or is this possible?

The original poster said that the guy's POI changed 4-6" when he removed the FH.

This says nothing about accuracy with or without the FH.

If he wanted to compare accuracy with and without the FH, he needs to shoot a group with it on, and then shoot a guorp with it off, and compare the group sizes (ie, maximum center to center distance for 5 shots).  

It makes sense than the POI changes when a muzzle attachment is installed, be it a comp, FH, or suppressor.

A properly designed and built F/H ought to not affect accuracy very much.   Some say that the Vortex increases accuracy.   I can't say whether or not that is true, but I've shot 0.5MOA groups with my AR10 with the Vortex installed.

My JP AR15 has shot quarter-MOA groups with the BC comp installed.

-z

ARL (APG) tested the older Vortex designs (G4 & G5) a while back, and I remember reading the results where when the systems were employed on an M-249 SAW, there was a dramatic improvement in accuracy.  On the M-4, M-16 and M-240 the older Vortex designs did not diminish systems accuracy in the least.  IIRC, the test was cut short due to some ammunition problems and the systems didn't get the full wring out they wanted for the night fire phase.  I thin k this test was about three years ago.   Also, either ARL or ARDEC -- can't recall, did some testing of a Vortex installed on an M-24 SWS about two years ago.  The test, conducted at JRTC for some reason, showed that the FH actually improved overall systems accuracy.  If you have contacted at Picatinny, you nmight be able to get more details.