I have a Zastava M85 that came with a barrel chambered in 5.56/.223. I wish to add a barrel chambered in. 300 BO. Unfortunately, I also have a South Bend Heavy 10 lathe and nothing but Imperial thread gearing. The Zastava action is threaded in M22x1.5 threads. I have measured it and verified it to be so. As a work-around, due to the limitations of my lathe, I am considering using a pre-threaded M22x1.5 fitting and internally threading it to receive a barrel stub which my South Bend is capable of producing. My question is, how to calculate the barrel wall thickness necessary to contain the 50,000+ cup pressure? Is this the hard way to do this? Absolutely. Would it be easier to find someone to thread and perhaps even chamber the barrel for me? Absolutely. But that's not what this is about. I'm out to learn a skill, not learn where to farm problem work out to. If anyone can assist with the calculations, I'd appreciate the replies. For the nay-sayers, flame suit on. Do as you see fit. Thanks.