I bought a 20" target/varmint heavy barrel from a medium size midwest manufacturer. Before install, I measured the chamber neck diameter with pin gauges and it was larger than I thought for an accuracy intent barrel. I sent an email to the company to verify the dimension was within their specs. They sent a drawing of the barrel external dimensions.

I replied I wanted the chamber dimensions, and could they sent a chamber drawing and tell me what reamer was used. They replied that was proprietory info.

My intent was to verify the chamber was within their specs and to do as much as I could do to assure the barrel would be accurate before installing and firing. I guess I'm pretty much on my own and will install and accuracy test. I'm pretty surprised they consider chamber dimensions proprietory since every one sold is able to be measured.

I'm of 2 minds on this.

On the one hand:

Apple refuses to give third party repair shops schematics. AS far as they're concerned the schematics for a particular Macbook considered to be proprietary information worthy of being kept under lock and key. Apple tried to shut a couple of companies selling schematics down in court and got their asses handed to them because while Apple's stuff is copyrighted and privileged information, that doesn't stop someone from buying one to tear it apart and map it out.

On the other hand I don't feel that should be held back as "proprietary information." I have long wanted a 224 Valkyrie (just because), and because of the teething issues the round had early on they updated the reamer. Well, as it turns out there are vast quantities of companies still using the original reamer for some reason. This means the only 2 ways I can know whether I have the updated reamer are to either 1) ask and hope they can tell me, or 2) buy the updated reamer and present that to my smith when I send him the barrel blank.

Chamber dimensions are nearly equal in importance to buyers as other listed specifications such as twist and barrel material. Why hide it from potential buyers? Make them buy a barrel and use cerrosafe to determine if it'll work for them? Maybe they just don't want you to know if the chamber is cut to their specifications.

Other option... Make a cast of the chamber.

According to this, it might have been chambered with a JGS 223 Wylde reamer:

https://www.ar15barrels.com/data/223-556.pdf

When I was shopping for a new barrel for my Savage, I chose Benchmark Barrels based upon a recommendation from a trusted gun builder. I asked about their chamber dimensions and they just stated that it was a "Gold Medal Match" chamber and wouldn't divulge any specifics other than their name for the specific 308 chamber that they cut.

I always check to see what a rifle is chambered in whether or not it's a standard common chamber or a specific modified print before I buy (ie, M118, M118LR, 223 Wylde, M852, 7.62 NATO, etc...). Knowing what I know now, and with the skillset I've developed, I just ask for an unchambered barrel.

I have a chamber I cut my 308's to for general use but it's much tighter than a standard 308. If the customer asks, I'll give him the dimensions (throat, freebore, leade angle)

Tony.