There might be an issue with cooling if you conduct sustained fire in a near vacuum, but even on a light barrelled AR you're several magazines in before that arises, and if 90 rounds of 5.56 hasn't solved your initial problem, melting the gas tube is the least of your worries 🙂
Yes, but that doesn't help. Sure, the gas surrounding your gun, which is what it relies on for barrel cooling, is cold, but there's almost none of it. Try cooling your g&t with a microscopic ice cube 🙂
There might be an issue with cooling if you conduct sustained fire in a near vacuum, but even on a light barrelled AR you're several magazines in before that arises, and if 90 rounds of 5.56 hasn't solved your initial problem, melting the gas tube is the least of your worries 🙂