Oversized 6.5 Creedmoor chamber question

#1
Measured Hornady factory 140 gr ELD Match loaded ammunition on the case just above the extractor groove. After firing I measured again. .003 expansion which seems way to much to me. Bought the rifle second hand with a Benchmark barrel chambered I assume to Sammi specs but really no way of knowing for sure. In all of my reloading I've always strived for a first firing on virgin brass of a case head expansion of .0015 or less, so this concerns me since it is a presumably safe factory load.
Would going to a thicker brass such as Peterson or Alpha help mitigate this problem?

Danny
 
Aug 7, 2014
742
44
28
Gillette, WY
#3
New Hornady 140 gr ELD Match factory ammo measured just above extractor groove average of ten cases: .46666 measured with my Mitutoyo Digital Micrometer.
After firing measured .46986
Expansion .00320
You're fine, brass comes underized, by Hornady manual, .470" in the area you described is spec.
 
Aug 7, 2014
742
44
28
Gillette, WY
#4
I'll elaborate more, you fl die will take the diameter back down slightly, but it would be rare for even an out of spec chamber to yield any problems till after the 2nd firing, unless it was one huge screwup.
 
Sep 6, 2006
2,092
250
63
Southern California
#5
Where exactly are you talking about on the case? In the pic below, everything right of the green line is unsupported and hanging in air. To the left is supported by chamber. If you’re seeing .003 to the left, you’re good. There is nothing but solid brass to the right(except for the flash hole). If you’re seeing .003 there, that’s a lot, but would have nothing to do with chamber dimensions.
 

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