David, you're fine, when it comes to gun laws now days it's better safe than sorry. Yes you can mount a red dot to a AR pistol without a tax stamp. You can mount a red dot, a scope, a red dot/magnifier or whatever other optic you wish without a tax stamp. Hope this helps.

Absolutely can add a Red Dot to an AR pistol, No Tax Stamp Needed!! Always better to be sure so your question is valid!!

David, yes Sir you can legally without a Tax Stamp. Red Dots are classified as a standard accessory so you will have no issues adding. Cheers and stay safe!

Yes! You can mount any optics (scope or red dot) on your AR pistol without the need for tax stamp. The only exceptions are stock (non pistol brace type) and verticle foregrip. I hope this helps!

David, no question is too silly. There are no restrictions against mounting a red dot on an AR pistol, no tax stamp required. Have a great day!