Could someone please recommend a good NJ legal home defense round in both .40 S&W and 9mm? The primary concerns would be over penetration as well as muzzle flash. My head is exploding reading about it so I would really appreciate the advice of someone who has already looked into this. Thank you for your help.

Here's a good guide to go by:

http://www.luckygunner.com/labs/self-defense-ammo-ballistic-tests/

Ill throw in my $0.02. I use Federal Hst 180 gr 40S&W. Seem to be lower flash than FMJ. Same recoil feel as my practice fmj. No issues in ~500 rnds Ive shot.

Personally I use Hornady Critical Duty. But Hornady Critical Defense may more suited for CCW pistols. Either is fine IMHO.

A 15 ROUND MAG?

3 1/2" slugs...

3 1/2" slugs...

I think you just answered exactly what he wasn't looking for lol.

 

It's a tricky issue for a 40 Cal. Any good expanding bullet can help with over penetrating and I think the critical lines from Hornady are developed to decrease muzzle flash.

Hornady Custom 124 grain XTP (standard load)  for the 9mm

Hornady Custom 180 grain XTP for the 40S&W

 

And, here's the reasoning.

Accuracy - There aren't any more accurate defensive bullets than the XTP.

Quality - Hornady makes very good ammo, using good components, brass, etc.

No fluff - They don't rely on marketing fluff, just solid bullet design and execution.

Very little muzzle flash.

Tapered nose feeds reliably in every handgun that I've used it in. The "flying ashtray" profile worries me in some handguns.

I have used the same bullet design while hunting for many years without a single issue in performance.

A 15 ROUND MAG?

Yes, Glock G22 and FNH FNS9