40 s&w barrel dimension specs?

I have been looking for what the maximum barrel diameter should be in a 40 s&w barrel. There are chamber specs but no barrel specs. Not sure if this is the right spot for this thread but seemed to me the people in this category would know or know where to find the answer.

The reason I’m asking is I just recently acquired a Glock 20 10mm and purchased an aftermarket 40 conversion barrel for it to save my precious 10mm brass. The new conversion barrel was a double diamond 10mm to 40 conversion barrel from the Glock Store. To determine the lead bullet size I needed to size to, I slugged the barrel and got .4045”. Now the chamber in this barrel was actually pretty good and tight but it doesn’t play well with an oversized barrel. There was no way of getting a .406” chunk of lead in a case to fit the chamber. I called the store for a return since this barrel was obviously out of spec and they told me it was fine. Yea, right.

Any way, just wanted to know if there was a maximum dimension for the max bore size.

Corsair, You are new here. The obvious questions one who doesn't know you would ask are how was the barrel slugged (including the alloy of whatever you slugged it with) and how did you measure and how good are you at measuring? No offense but we can't judge with this little information if the barrel is really out of specifications.

I have never seen a maximum bore diameter for the 40 S&W or the 10mm. The nominal diameter of the barrel should be .400" groove to groove and have seen barrels exceed this by only .002". My Steyr M-40 measures .400" and my Kahr CM-40 measures .401". I am not saying that yours does not measure .406" but that I have never seen a maximum specification.

https://saami.org/wp-content/uploads...sting-Copy.pdf

Page 51 (60 according to the PDF software) groove DIA .4005 +.004/-.0000. Looks like they are in spec, but just barely.

I wouldn't be impressed.

https://saami.org/technical-informat...mber-drawings/

Sorry fellows. I forgot my password and never had access to the email with the old account. Formerly flybyjohn. Not a super active member but have been shooting my own cast coated bullets for quite a few years now. The slug was made from a stick on wheel weight and pounded through the barrel with a brass rod. It measured on a micrometer to the specs mentioned. I have measured my other barrels the same way and the Tristar/ canik measures .398”. The beretta elite measures .402”. And the stock Glock 10mm barrel measures .4015”. This new double diamond barrel came in at .40435 to .4045 depending on which grooves are measured. I would show a picture of me measuring it but not sure how to load one.

I finally got logged in with my older username. My email was set as my work email and the spam filter was kicking it out. Still cannot get my ipad to work with it but my computer works fine. So I am going to ditch the Corsair user name now and go back to the flybyjohn user name.

Thanks Kenton for the info from those pages, I think I came across that in my searching for answers but wasn't sure that the barrel fell in with the +.004 since it was under the heading Chamber.

I was able to return it to the Glock Store on their dime after an hour of conversation with them, with the condition that I am never to do business with them again.

Quote:

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Originally Posted by flybyjohn

I was able to return it to the Glock Store on their dime after an hour of conversation with them, with the condition that I am never to do business with them again.

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Not a big loss there. I wouldn't buy anything from them anyway, as the guy who runs it acts like he is the all knowing Glock Guru, but doesn't even have a proper grip on his guns in his videos..

When I see the muscles in your forearm flexing as you are clamping down on the grip it reminds me of my Second Front Sight Class where the instructor asked me what I was doing when I was doing the same thing and was completely missing the target that was 5 yards away from me. He does the same thing and the only thing it accomplishes is to make your arms so tired they want to fall off your body.

His Glock Mod Videos are full of assumptions that he has made that are so far away from proper Glock Armory, it is ridiculous. He thinks he knows what he is talking about? Closer examination proves otherwise.

I have listened to him pontificate at the SHOT Show while walking by his booth. When you insert a .50 cent word in every Sentence to act like you know what you're talking about, it just proves you don't!

My .02 on the Glock Store!

Randy

I am after a KKM barrel now. I kind of wanted a conversion barrel to take the g20 down to a .40 and then throat it so that it will take 10mm length loads. I didn't want to throat the kkm barrel for fear of messing something up. Brass is just so hard to get for the 10 that I hate to shoot it, but if I could shoot 10mm power loads in the throated .40 conversion barrel then I would be happy. I have shot the extended .40 loads out of the 10mm barrel but hate having to scrub the chamber so hard to remove the carbon deposits it makes before going back to 10 brass. I think at this point, I will just get a 6" 10mm kkm barrel and shoot less.