![Glock polygonal rifled barrels Glock polygonal rifled barrels](https://www.all4shooters.com/en/shooting/pistols/glock-barrels-polygon-rifling-analysis/glock-barrel-1.jpg?resize=bec91f:250x&cid=20e.4p1)
While spending some time surfing around gun boards over the Internet, I had the stupid idea to intervene on a thread focusing on whether the barrel rifling profile found on the Austrian-made Glock pistols is indeed Polygonal or not.
A newbie asked about the correct definition of the barrel rifling profile found on the 9mm Glock 17 semi-automatic handgun.
The result sparked a long and intense debate − although always kept under friendly terms − between those who claimed that Glocks sport a "pure" Polygonal rifling, or a semi-polygonal rifling, and others adopting different (and sometimes fancy) definitions.
![Glock polygonal rifled barrels Glock polygonal rifled barrels](https://www.all4shooters.com/en/shooting/pistols/glock-barrels-polygon-rifling-analysis/glock-barrel-2.jpg?resize=ae282c:250x&cid=20f.4p1)
The rifling profile should always be considered as being composed by rectilinear segments (the lands) intertwined by circular arches (the grooves); in my opinion, following this description, the Glock pistol barrel configuration should be described as "semi-polygonal rifled".
However, upon close observation of Glock barrels, it would seem that the lands would consist in convex surfaces − basically standard-tipe rifling lands deprived of their typical corners, or "rounded" as they've sometimes been described.
Furthermore, after recovering several bullets fired from a Glock 17 through water jugs, upon their examination I had the distinct feeling of finding myself in front of a gun barrel whose lands were nothing but flat surfaces, and thus whose rifling profile consisted in six simple straight lands intertwined by six circling arches.
![Glock polygonal rifled barrels Glock polygonal rifled barrels](https://www.all4shooters.com/en/shooting/pistols/glock-barrels-polygon-rifling-analysis/glock-barrel-3.jpg?resize=3f88bb:250x&cid=20g.4p1)
The thing left me quite puzzled, and my impressions were later confirmed when I used some soft cast lead to obtain a mold of the barrel bore.
As far as it concerns the difference between the bore as it really is and as what it appeared to me at a first glance, I first thought it was due to some kind of optical effect due to the fact that the flat surface follows a helical pattern around a cylinder − an assumption that's considered likely by several physicists specializing in optics (and by many amateur enthusiasts of the same matters)... at least until my friend Franco revealed the "riddle": the solution was extremely simple, if not outright trivial, as usual.
As a matter of fact, every Glock barrel 'business end' features a crowned muzzle: the bore is flared in a perfectly conic way, and what we actually see is the intersection line between the conic flared surface and the flat surface of the rifling lands.
![Glock polygonal rifled barrels Glock polygonal rifled barrels](https://www.all4shooters.com/en/shooting/pistols/glock-barrels-polygon-rifling-analysis/glock-barrel-4.jpg?resize=8726b9:250x&cid=20h.4p1)
Back to the BBS thread... the thing would probably have ended there, with all participants firmly standing on their own opinion, until a supporter of the "opposing position" − stating that the Glock company claimed that its barrels are "polygonal rifled" only and solely for marketing reasons, while there would be no polygonal rifling or semi-polygonal rifling at all − went on to support his "motion" by posting a few pictures (some actually very well made!) stating that "a picture is worth a thousand words".
While it's generally true that a picture or a simple drawing may normally be enough to clarify, in this case his camera − and thus the pictures he took − were affected by the above-mentioned optical effect caused by the lines intersection; the fact that they supported the wrong thesis at the poster's eye made the error even more severe.
At a close glance of a Glock 17 barrel rifling, an acute eye will notice how the rifling lands − if looked at from a parallel position to the barrel axis − will look like straight lines that will seem to turn into curves as soon as the point of view is tilted away from the longitudinal axis of the barrel itself; unfortunately, that was the point of view from which the board member had snapped the published pictures.
![Glock polygonal rifled barrels Glock polygonal rifled barrels](https://www.all4shooters.com/en/shooting/pistols/glock-barrels-polygon-rifling-analysis/glock-barrel-5.jpg?resize=d686e7:900x&cid=20c.4p1)
At this point I had been enticed enough, and wanted to provide some correct information to the board members still engaged in the thread concerning the barrel rifling profile.
![Glock polygonal rifled barrels Glock polygonal rifled barrels](https://www.all4shooters.com/en/shooting/pistols/glock-barrels-polygon-rifling-analysis/glock-barrel-6.jpg?resize=651765:250x&cid=20k.4p1)
I thus field-stripped my Glock 17 and recovered the barrel bore molds I had previously obtained through soft cast lead. I then scanned the barrel and the molds through a profile projector and a dissecting microscope; after a thorough 20x magnification transparency projection and episcopic illumination procedure of the molds, some recovered bullets and the barrel, and after using an automated fiber-optic measuring system, I came to this conclusion: the Glock 17 semi-automatic pistol barrel features six straight lines akin to the six sides of a hexagon, intertwined by six circular arches, and that means it is indeed a Polygonal rifling.
If you own a Glock 21, Glock 37 or any similar handgun, don't fret: the .45 ACP and .45 GAP Glock models will have eight barrel grooves instead of six, but will still be using the polygonal rifling design.