The scenario:

HD/PD with 16", 1:9 twist, 'post-ban', non-suppressed, CQB configured AR.

The questions:

1) I'm considering purchasing some 75 gr. TAP to load in my 'primary' mags. Regardless if my barrel can stabilize the bullet, is there practical reason to be concerned about 'bullet stabilization' in close range engagements?

2) Can anyone attest to the low flash signature claims Hornady makes regarding this ammo, and is it diminished enough to have any significant benefit out of a non-suppressed rifle in low or no light encounters?

What do you consider "close range"?  If you talking about normal room size areas, then you don't need to really be worried about tumbling, from an accuracy standpoint.  Otherwise, if the rifle can't stabilise the bullet, you're going to have groups akin to shooting a smooth bore, if not worse.

Alot of the 1in9's will stabilize the 75 gr TAP round.  If yours won't, My suggestion is to maybe try something in the 68 or 69 gr range that will stabilize and still have the terminal ballistics that you are looking for.

I have no experience with TAP in low light so I can't answer your second question.

Quoted: 1) I'm considering purchasing some 75 gr. TAP to load in my 'primary' mags. Regardless if my barrel can stabilize the bullet, is there practical reason to be concerned about 'bullet stabilization' in close range engagements?

Two that I can think of
1) Potential lack of sufficient penetration if the round strikes sideways rather than nose first.

2) Accuraccy bad enough to miss depending on the target.

Can anyone attest to the low flash signature claims Hornady makes regarding this ammo, and is it diminished enough to have any significant benefit out of a non-suppressed rifle in low or no light encounters?

Yes it's low flash - as is Black Hills.  Definately the type of ammo you want to use if you are not allowed a flash supressor.

Tried some 75 TAP in my 16" bushy(1:9) the other day at 100 yrds.  Was crossing my fingers but to no avail.  My groups were quite erratic,.  Conversly, had no problems with 55 XM193.  Will by going to a lower weight and see what happens.  Did not spend that much time at 50yrds so unsure at what distances i would feel comfortable in using that weight in a self defense situation.

Use the XM193 if you have no problems with it.  It will work just fine.

If you can't stabilize the 75gr OTM, then use the 68gr OTM (Heavy Match) from Black Hills.  The 68 gr is still much better than the XM-193 with respect to terminal performance and flash.

Thanks Forest.  It's what im gonna try next.

I've used alot of the TAP stuff in both .223 and .308. We are going to the 168 grain TAP for our Remington bolt guns. I've been pretty happy with it. It crono's very consistantly.  One thing to consider though, If you run the round through your gun and say you aren't worried about the long range accuracy, in theory that is fine. Just remember you may have to defend your choice in court some day. Such questions may come up like what is your accuracy standard for your department and does this round meet it. Just some things to think about. Hey this is my first post! Hi all!