Yes, that is a big problem when non-technical people get stuck dealing with technical issues. I'll bet your foreign customers don't even have engineering support to answer your questions.I’m dealing with this headache right now with an overseas customers for finished M40 sniper rifle barrels for they’re military. The order is for two batches of 350. They’re prints don’t show enough detail when it comes to the chamber. They call it 7.62x51mm. So I’ve sent them several different prints for them to tell me which reamer to use and no one at the arsenal (can’t talk to anyone directly as is has to go thru a contractor which no one there knows anything about guns) can tell me which exact chamber spec it is!
If it helps, the USMC M40A3 barrel drawing specifies the chamber dimensions shall conform to ANSI/SAAMI Z299.4, .308 Winchester.
There is also a mistaken belief that one chamber fits all. If you read various reports on weapons development tweaking the chamber dimensions has a great impact on weapons' reliability. In some cases the difference is between acceptable and unacceptable performance. For example, during WW2 the British got acceptable performance out of the Hispano-Suiza 404 20mm, but the US never did, and the Brits were convinced the reason was the US never adopted the British chamber. This was particularly vexing for the British as the US was supposed to be a major supplier of 20mm aircraft cannon, but poor reliability relagated US made 20mms to training use only. In fact, a majority of US produced 20mm cannons were placed in storage and never used.