I am at a dilemma... At the moment, I have a S&W M&P15 with a few goodies.  The only problem is that I barely get to shoot it, to solve that I purchased a Tacsol 22lr upper which I love.  I REALLY like shooting the .223 but the closest outdoor range is about an hour away (and it is nothing special)  There is an indoor range that allows me to shoot but it is only 25m.  I have been tossing the idea around about getting a complete 9mm (spikes) but to do so, I would most likely have to sell the m&p... I could keep both, but its just a bad financial move (I am a student).  What I want to know is, hows does shooting the 9mm AR compare with the .223?  How far is the 9mm accurate?  How is the kick compared to the .223?  What is the stopping power loss going from the .223 to the 9mm (in case the zombies to actually attack lol)?  Would I regret this decision?  Thanks for the input.

I shoot my 9mm's at 25-50yds, very accurate, I'm not sure what the maximum effective range would be, I think I read somewhere it is like 150yds, more of a close range CQB type gun. Felt recoil is about the same. If I only could have one it would be a 5.56, much more effective at any range compared to a 9mm if your worried about zombies . However the 9mm is much cheaper to shoot.

No way would I flip a 5.56 for a 9mm.  Wait until you can afford it.  Buy a hi-cap 9mm pistol.

Just save up the money to get the 9mm AR!

You could get a complete 9mm upper, throw a DPMS hammer in your current lower, swap out your buffer for a 9mm buffer, and use a mag block that is easily removable, and then just swap uppers as needed.

The DPMS hammer would work with 9mm uppers (Colt style) and your M&P15 upper.  A 9mm buffer would still work with your M&P upper as well (and maybe even increase performance).  Then you pull the mag block, pull the 9mm upper, throw your M&P15 upper on, and your ready to shoot 5.56 again.

Just another option to keep in mind.  It would save a little money, because you'd be using the same lower for both setups.

The way my 9mm AR is setup right now, I can pull the mag block, swap uppers and I'm ready to go.

To me, it seems like the 9mm pushes back more than a 223.  Maybe it has to do with the heavier bolt and buffer.

Yeah, that and straight blowback.

It seems like 9mm has a longer recoil impulse than .223, sort of like the difference between a tube gun and a rifle.

Personally, I was waiting to get my RRA 9mm back so I could sell it off, but now, well, an AR is an AR. I just need to get more mags for it.