Just ordered a M&P 15 sport, and know zippy d doo da about this rifle, except that I've wanted one for a few years now

I know the twist is 1:9?, and a bullet grain weight of 40-69gr would probably be best for this slow twist rate according to another thread here.

I'm looking online at bulk ammo sellers, and am trying to decide what to buy for the rifle.

5.56x45?...is that the same case dimension as .223, and can I shoot it in the 15 Sport?

Any recommendations on ammo for this yet to arrive rifle would be greatly appreciated.

I'll be using this ammo for target/fun shooting at the range, and don't want to buy 500 or more rnds of any stuff that won't work especially well in the M&P, or that might prematurely wear the action with steel cases.

Also, for those of you that might be using the M&P 15 in the home (protection), any defensive ammo (or other recommendations for accessories, lights, sights, etc.) would also be appreciated.

Thanks for your help.

If you go the the S&W website and check out modern sporting rifles, you'll note that the caliber for the Sport is listed as 5.56mm. The 5.56 x 45mm is assumed.

1-9 really isn't a slow twist rate, it'll handle up to 75 gr HPBT bullets.. The .223 debuted with a 1-14 twist rate. That was later changed to 1-12 because of bullet yaw at sub-zero temperatures. The military 1-7 twist was dictated by a perceived need for a 5.56mm tracer round.

You can use heavier bullets they just might not be as accurate but try them anyway because each rifle is different. And you can use 556 or 223

Google XM193. It's 55gr FMJ brass cased ammo from Federal and you can find it for $0.33 per round or less right now. It's not the most accurate ammunition because it's loaded to past military specifications, but it's adequate for the range and it's inexpensive. I shoot my own handloads for any serious purpose, but still keep a couple thousand XM193 on hand.

Defensive ammunition and setting up the rifle have been discussed ad infinitum and deserve their own thread. Use the search function and post if you have any specifics.

The original .223 Remington has a slightly lower powder load than the 5.56 and the 5.56 has a slightly different neck measurement. See: .223 Remington - Wikipedia, the free encyclopedia

My M&P15T, SKU811041, has a 1:8 right hand twist. My research indicates the faster the ratio the heavier the bullet can be. Common ratios now days are 7,8,9 to 1. As far as my testing goes to date, using factory, standard load PMC rounds of 55, 62, and 68 grain bullet weights, the 62g is best thus far. If this changes, I'll post up my results.

I'd go for whatever you can find cheapest in 5.56 or 223 (Steel or brass). At home defense and plinking distances you won't see much difference in accuracy, imo. The cheap stuff will allow you to buy more to practice with. Buy a few mags worth of good stuff for defense if that's what you'll be using it for.

i have shot the cheap stuff through my sport for quite some time now, and as long as you dont mind cleaning it for an hour, maybe two, then there is no problem. This gun loves dirty ammo. Just keep her lubed.

Thanks for your replies. I started this thread pretty late last night (after placing the order) and I hadn't even started to search for basic information on the rifle, ammunition, or accessories.

Usually, I don't buy a firearm that I don't know much about and haven't done some studying up on, but I've always liked the S&W products I've owned, and since I'm just looking for a basic .223, I'm really looking forward to its arrival!

Can any of you suggest a good, spare magazine that'll be used for defensive rounds?

I'll do as suggested and search for the basic information on the care and feeding of the Sport, and if I have any more specific questions that I can't find the answer to, I'll throw them out to all of you here.

Thanks again.

PMag is always good. Used them in some harsh climates and abused the **** out of them and never had a FTF with one.

Cant go wrong with Pmags. Also Walmart is selling ZQI all brass 5.56 62 grain for 9.97 per 30 rds. Shoots great out of my Sport.

I won't use anything other than Pmags. I figure there is a reason my AR came with one.
When I got my grown up AR I bought a thousand rounds from Bulkammo.com. I got 55 grain boat tail .223 PMC ammo for about $355 including shipping as I recall. You can shoot .223 or .556 through a .556 rifle. But you can not shoot .556 out of a .223 rifle.

Simple plinking ammo, $325/1000 shipped.
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