Ah! gas port diameter on the IURs is similar to those of the MK18s. I believe right around .070 plus or minus - not sure of the exact measurement as I haven't taken any off of my IUR.
Throat erosion will of course be somewhat unrelated to the gas port diameter - assuming you are referring to the throat of the chamber.
Gas port size is an interesting topic. You need to take a broader view of why and how a gas port size is chosen. Ultimately, no one will argue against wanting a service-based rifle that is ultra reliable. In that case, a slightly larger gas port is advantageous even if it means the system is "over-gassed" with a suppressor (I quote that because over-gassed is only relative). If you were running a system with a suppressor 100% of the time, then perhaps a slightly smaller gas-port would be better suited - but in that case you can design the gas port etc. within a closed system of a suppressor.
It is also important to know that generally speaking, a military based system has complete control over the barrel, chamber, gas port, gas length and most importantly; the ammunition. I think a lot of people tend to forget that service based firearms have a closed-system of ammunition; in that the firearms are designed to operate within a range of pre-determined ammunition specifications. Of course, they also want the system to function under austere conditions - does a larger gas port and shorter gas system contribute to premature wear vs. a mid-length system? That is entirely possible... however, having a system that functions regardless is far better than a marginal enhancement in over all service life.
When you look at the commercial market, what the individual chooses to shoot their rifle is wide open. It may be high-pressure Norinco, or other commercial loads of varying degrees of quality. In that case, a barrel using a larger gas-port would be excellent - you'll see reliability across a broad spectrum, which is what both the manufacturer and the end-user would want. Furthermore, most individuals would never see, feel, or understand the difference of over-all-lifetime by using a larger gas port vs. a smaller one, but they sure as sh*t would complain if their rifle didn't function.
Another consideration is how much ammo could you shoot through a given rifle, where you notice additional wear on the bolt and carrier? Probably an obscene amount and at that point... the replacement cost of a bolt, carrier, and barrel will still be so low compared to how much you spent on ammo... that it's probably not worth it.
Lastly, the buffer is an important part to consider. All Colt Canada rifles run an H2 buffer. I would much prefer to have a rifle that might be slightly over-gassed, and use a heavy buffer than one that is perfectly tuned, which may experience malfunctions under even prolonged shooting, with minimal cleaning.
You are also correct in that the straight gas tube, at least with the Colt Canada set up allows for the armorer to change the gas tube without removing the barrel/gas block - however I believe that to be an additional positive, alongside the the primary aspect of enhanced service life.
Drop me a PM if you wanna discuss further too! Hope this provided some insight for ya.
