Ten Percenters

If just one gun owner in 10 is in the NRA, and there's 6 million NRA members, that's 60 million gun owners.  h/t Miguel.

Let's take that as a given.

Let us also take as a given that the threepers are correct about how many people will be shooting come "The Revolution™"

3% of 60 million is 1.8 million people.

How big is the military and how many cops are there again?

The FBI says there's about a million people employed by the various law enforcement agencies across the nation with 698 thousand being sworn officers.

Active duty, national guard and reserves total just over 2.2 million people.

Side note:  It takes just over 13 troops per 1,000 population to effectively keep a lid on an insurgency.  That would take about 3.9 million troops worth of "boots on the ground" to accomplish in the USA.  Guess how many troops are needed to support these boots on the ground.  Eight per combatant.  That would mean the US military, fully deployed, would need to be 35.5 million strong.

Notice, also, that the 13 troops per 1,000 population is irregardless of how happy the population is with the troops and the state of affairs that lead to there being an insurgency in the first place.

 Also note that the recruiting pool for the military is from the very people who're most likely to be insurging (totally a real word I didn't just make up).

You'd have to establish a draft and have an effective means of filtering out potential insurgents.  Good luck with that!

The math doesn't look good for our intrepid tyrants.