I have run them for thousands of rounds without cleaning the gas tube but, if you run surplus or Wolf it could clog sooner. I don't have a lot of spare time so I use brake cleaner followed by a shot of WD40, the WD evaporates so it doesn't gum up like an oil would but, to answer your question as preventative maintenance every 4-500 should take care of it easily.
The 6.8 is the fastest growing cartridge and #1 choice for hunting deer and hogs with an AR15.
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