After taking the Semper Paratus AR-15 Armorer's course last weekend, I started wondering about what gas port sizes different barrel manufacturers use, especially in the context of building rifles or diagnosing gas issues. This wound up being an interesting side project for lunch breaks at work, as I spoke on the phone or via email with representatives from 17 different companies who manufacture their own barrels, and discussing the topic of gas ports on the Facebook side of the house. I figured out fairly early that if I phrased the question in the context of building a rifle with the company's product, I got better responses than if I just flat out asked the question. I suspect that what I was told on the phone by reps and what a pin gauge set would tell me about these barrels would not always be the same spec, especially with certain companies who have documented QA/QC issues and who are more interested in selling guns than providing a top quality product. This suspicion is further confirmed by Michael from Sons of Liberty Gun Works, who posted a photo of actual gas port dimensions which have come through his shop--some of the variances were huge, even between barrels from the same manufacturer. The next step in compiling information on gas ports would be to start actually using a pin gauge on barrels and recording the results, and comparing those measurements to what I was told by representatives of these companies. Here are some common themes I saw this week: -Rep thinking I was talking about the diameter of the barrel at the gas block -Once that issue was cleared up, being transferred to a desk where I left a message and was called back -Tech acting very puzzled about why I would be asking him this question. Some highlights: -Gene with LMT saw my initial post on Novice/Intermediate, so when I called him, he knew what I was up to. I was used to catching techs off guard with the question, instead he caught me off guard with his answer. -Michael with SOLGW posting the entire list of gas port dimensions on Novice/Secondary, with the caption "We ain't scared." -"Izzy" with Invincible Arms (who studied under Eugene "Gene" Stoner, according to him) acting very, very suspicious about why I would be asking him this question. I spoke with him for about 10 minutes about ammunition differences and gas port diameter before my lunch break ended. -Josh at Criterion handling an odd situation with grace, as he needed permission from Midwest Industries to release the gas port dimensions to some random knucklehead on the phone. -BCM responding to my email with a statement saying their gas port size is proprietary. I happen to have a 14.5M barrel sitting on my desk--the gas port is .076". It boggles me that something so easily confirmed would be considered proprietary. -No, I don't know that. I don't think anyone knows that." -Sig Sauer representative.