Here is information about the various roll marks you may see on Glock barrels, slides, and/or frames.
The pentagon indicates polygonal rifling, which all Glocks except the 17M and 19M use. Those two use land & groove rifling (a requirement under the FBI contract). A pentagon without a dot in the middle means the barrel is from grade 5 steel. Pentagon with a dot in the middle indicates grade 6 steel. Neither symbol has anything to do with +P and/or +P+ compatibility. For +P and +P+ info, see https://us.glock.com/customer-service/faq. The Austrian government eventually required the 3D in the oval, which replaced the pentagon symbols. NIST (National Institute of Standards and Technology) created a 3D ballistics database for research to positively identify bullets fired from specific barrels. The 3D database will help draw positive matches between a fired bullet and the barrel it was fired from. Barrels marked with a 3D are in the database. Ballistic experts can strategically identify the correct source, but it’s not 100% accurate. For more info about the database, see https://www.nist.gov/news-events/news/2016/07/nist-3d-ballistics-research-database-goes-live. It’s important to note that the evolution of these symbols should not be interpreted as there are issues with the components with previous marks.
The “AT” indicates it was made in Austria. Newer barrels made in Smyrna, GA have a “US” and a little outline of the state of GA.
From 1982 to 1991, Glock 17 pistols were assembled & test fired in Austria. (Later pistols were also assembled and test fired at Glock Inc. in Smyrna, GA.) Those barrels have an eagle roll mark. The eagle with the number 2 in the center is Austria’s coat of arms. The number 2 in the center of the coat of arms means it was proofed at the firing proof house in Vienna, Austria. You’ll also see this mark on frames from the same period.
The ‘NPv’ is the Vienna proof house roll mark for ‘smokeless powder proof for parabellum pistols’. The pistol was tested using a round loaded to at least 130%. Normally, Glock guns are tested with 120% loads. The markings are proof marks and inspectors marks as required on Austrian pistols that they met the 130% requirement. Many of those NPv marked guns have “Glock Inc, Smyrna GA” stamped on the bottom of the trigger guard.
Sometimes, you’ll see three letters after the NPv on Austrian made barrels. Those are date stamps to indicate when the BARREL was test fired (note that does NOT necessarily mean when the pistol was built). Eventually, Glock did away with those three letter codes. Unofficial information I have to decipher those three letter codes that are on the barrel (not the serial number) are:
The first letter is for the month:
The last two letters are for the year:
For those with the ‘CIP over N’ roll mark, see https://en.wikipedia.org/wiki/Commission_Internationale_Permanente_pour_l%27Epreuve_des_Armes_%C3%A0_Feu_Portatives and http://www.mdwguns.com/cip.html
Gen 5 pistols have a ‘5’ to the right of the ‘3D’ mark on the barrel. ‘M’ guns have a ‘5M’ to the right of the ‘3D’ mark.