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Odd, but consistent groups that I can’t explain


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I am getting some very odd groups with my new custom Aero Precision M5, in .308 Winchester. With several match grade factory loads at 100 yds., I am getting three rounds of a five round group that are a cloverleaf measuring ~ .25” center-to-center, with the other two rounds high and expanding the overall group to ~ 1”x1”. I have gotten these virtually identical groups with Federal 175 7.62x51 MK HPBT, Nosler 175 Custom Competition, Barnes 168 TTSX and Lapua 175 Scenar-L.

The groups are fired semi-auto, magazine fed. The groups have all been fired at about the same pace: one round every 30-60 seconds, so no significant heat-cycling of the barrel. I am getting the same results from multiple different magazines  — all Mag-Pul — 10 round, 10 round with -5 round limiter and 25 round M118LR magazines, so I can’t attribute it to a specific magazine. The barrel is a Criterion 18” Hybrid; comp is a Precision Armament M4-72; BCG is JP Low Mass with a JP Enhanced bolt; optic is a Trijicon Credo HX 2.5-15x56mm. I have duplicated the same results on different trips to the range. 
 

I am at a loss as to explain how I could be getting 3/5 rounds in essentially one ragged hole and the other two high “flyers”, with multiple different factory loads. Any ideas?

CBA63ADC-1431-4E06-BD64-931ADA6DDE39.jpeg

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3 hours ago, Armed Eye Doc said:

Is it the difference between left and right side of the magazine?  Try one round in a mag for each of five shots so they all come from the same side.  

That is what I thought it could be; I am getting the same results using multiple different magazines, so if it is related to the round being chambered from one side of the magazine, and it’s not the magazine itself, I wonder if it could be the barrel feedramp???

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1 hour ago, LensWork said:

...so if it is related to the round being chambered from one side of the magazine

That will immediately indicate an issue with the ejector face...

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P-Mags.  First round is left, top round is right - always - like it should be in a mag. 20 rd mag, last round is right.  30 rd mag, last round is right.  Been that way for decades, before Big Army fucked that up.  Ignore Big Army.

You loaded 5 rounds, in a P-Mag.  First was left, etc.  5th was left.  No other way around that.  It is what is is.

You had 3 rds clovered. You had 2 rds out, but close (but you haven't posted any pics or your groups yet...  just of your pretty gun...)...  <<<  BIG deal right there. Get your group pics up.  Post 'em.

You have a problem with the profile on your ejector face.  Nothing more. 

Post pics of the face of your ejector, so we can look at it. 

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