Get a Ceiner conversion kit. That will allow you to shoot .22 LR- this will afford you more practice (.223/5.56 ball isn't as cheap as it used to be). It could also be useful for small game hunting.
Great advice, and I plan on getting another one as well. Black Dog Machine (LLC) makes some great full-size magazines that work with the Ciener as well...but either way the .22 LR conversion is great for plinking, practice and will easily take squirrels at 25-30 yards.
Just returned from 14+ months in the sandbox, and the M4 is alive and well and doing great. Best thing about that platform is that you can easily go from .22 LR (Ciener in the .223 barrel) up to .458 SOCOM or even .50 Beowulf for some real punch; but more importantly uppers in 6.8 Remington/SPC and the 6.5mm Grendel are excellent rounds with a little more weight and power further out than .223. Just add another upper/bolt (maybe a few magazines if needed) and choice of optics and you have a great modular gun that can plink, do CQB, reach out to .308 distances or stop stampeding buses.
I would strongly recommend the .22 conversion for practice. As far as effectiveness of the .223, if you practice and are accurate, it will be more than enough for 99% of game/threats in the lower 48 out to 250-300 meters. Depending on the state, it may be an issue for hunting, but that's where a good upgrade/addition to 6.Xmm comes in handy.
Plenty of options and a good choice. There's a lot of opinionated debates on caliber, action, penetration, etc., but from my experience, if you can accurately hit your target, a .22 LR is more than adequate.
Buy ammo, enough magazines, a few spare parts and plenty of range time...enjoy and Happy Holidays!
ROCK6