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Old 02-17-2012, 20:45   #1
PettyOfficer
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Pentagon Proof Mark?

Does the pentagon proof mark have a significant meaning?
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Old 02-18-2012, 00:25   #2
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http://glocktalk.com/forums/showthread.php?t=1191908
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Old 02-18-2012, 01:42   #3
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I had searched 'proof marks', guess I didn't use the right terms.

That thread was useless, nothing but speculation and smart alecks.

Last edited by PettyOfficer; 02-18-2012 at 01:49..
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Old 02-18-2012, 07:55   #4
MakeMineA10mm
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It is a German/European means of signifying a polygonally-rifled barrel. My HK45 has it on the side of the barrel exposed through the ejection port when in battery also. Most, if not all, of my (Austrian) Glocks have it also. Over the last few years, Glock has dropped a lot of the European features (markings) for US-destined pistols. Austrian proofs went a long time ago, more recently the "US" suffix at the end of the serial number went, etc.
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Old 04-24-2014, 13:13   #5
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Sorry to revive an old thread, but since I just recently came across a bunch of stuff on the interwebs regarding these, what they meant, and if they referred to chamber support... here is an answer straight from Glock technical support:

Pentagon = grade 5 steel
Pentagon with a center dot = grade 6 steel

Does not indicate anything regarding chamber support, and he said that chamber support was not changed from gen 3 to gen 4, which is something I've read a lot of people claiming. I don't have a gen 3 to check, but my gen 4 G22 seems to have much improved support from other older model barrels that I've found pics of.
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Old 05-05-2014, 01:16   #6
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That's the best explanation of the pentagon I've heard, thanks for sharing.
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Old 05-05-2014, 05:51   #7
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Upon looking further into steel grades, it got way over my head as far as metalworking knowledge, and I did not find anything directly referencing "grade 5" or "grade 6" steel as it pertained to gun barrels. Suffice it to say, the pentagon with a dot indicates a higher grade steel.
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Old 05-05-2014, 19:25   #8
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Makes sense to me. I've noticed on my newer Glocks, with the dot...There is a mark on the breach face from contact with the barrel. My older non dots, have no breach face mark. Makes me believe the dot barrels may be slightly harder.
Obviously I'm no expert, just observations. Your explanation makes sense. I never bought into the pentagon being a sign of polygonal rifling.
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