I use an adapter that is made by GG&G. I don't know about attaching it to the gas block though, I am interested in finding out about a way to use my GG&G mount without having to drill holes in my hand-gaurds. I have it mounted to the handguards on one AR, but I just got a Colt LE 6920 and I don't want to permanently alter the handgaurds. Anyway, the GG%G mount works great and I love the M-6 for my ARs. It works great, is very ergonomic, is not bulky or gawdy and can be removed for use on other weapons easily. I use it on my glocks as well.
The only thing to look out for, make sure that you get a mount that is made for the streamlight. I have heard of people trying to mount in directly on forearm rails and other mounts that weren't designed for it and it stretches out the mounts on the light so it won't fit your pistols or anything anymore.
Any ideas on how to mount the streamlight without permanently altering/damaging anything? I don't want forearm rails or anything either. I like my weapons stock (for the most part
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