on my M&P 15 sport the barrel is stamped 5.56 NATO 1/8 5R.
what bullet weight does this rifle shoot the best in 5.56 ammo? if i run .223 thru it what bullet weight should i use?

i would like to hear some opinions please. what do you guys think? thanks

The sport will eat anything. I shoot steel cased ammo because its cheap with zero problems.

Any ammo will be fine in your barrel. Barrels, however, are like snow flakes - to the naked eye they all look the same but there are microscopic differences that make them each unique. The only way to know which ammo your particular barrel likes best is to try a great variety and see which gives the best results.

Generally speaking, the more expensive rounds should be more consistent, as they have tighter tolerances for all things considered and most likely use better (lower flash, cleaner/faster burning) powders.

However, I bought a 5.56/.223 specifically so I don't have to pay $1+ a round, so I shoot the cheapest brass cased I can find. I'm mostly just target shooting/plinking or practicing where MOB is sufficient. Steel cased is fine to shoot, I'm just OCD about a clean gun and the steel stuff is so dirty.

My gun really likes the Winchester 5.56 55gr FMJ, but I also shoot a ton of .223 fiocchi, PMC bronze, and American Eagle cause it's cheaper and still gives me good, consistent results. I stick to 55gr because a scope I sometimes use has BDC for that particular round.

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686/M&P9 Pro/M&P15X/M&P15-22

Currently you shoot whatever ammunition you can find. The 1/8 twist should shoot everything except 80gr bullets (a handloading proposition only) well.

As mentioned, shoot whatever reasonably priced ammo you can find. No need to cycle the expensive stuff as the sport will eat up steel ammo with no problem.

As far as the specifics go, I tend to stay with 55g and 62g ammo, but that's what you're most likely to find anyway. I don't care if the ammo is .223 or 5.56 when I'm shooting paper.

like TheMaineEvent said, anything with 55-62 grain is fine. Although I hear you need to clean more when shooting steel case

I stay away from the steel cased stuff because the bullets aren't jacketed in copper. Their jacketed in a bi-metal. It will wear the barrel faster because it isn't as soft as copper. The barrel is a wear item. But, if I can do anything to increase its life I will. Good luck with whatever you decide to shoot.

I'm going to call you on that one. Increased barrel wear is an Internet rumor. The soft steel jackets are much softer than barrel metal. The U.S. government used gilding metal clad steel jacketed M2 Ball for years and their studies (Frankford Arsenal in particular) showed no more wear than gilding metal jacketed bullets. Besides, chrome lined barrels or Melonite treated barrels are much more wear resistant than plain barrel steel.

I based that opinion on this article. Only comparison I have seen. Looked like they were pretty thorough to me. Why chance it. At any rate he can read this and decide for himself. Either way his gun/barrel. Like I told him before Good luck with whatever he choses. I realize that most people will never shoot as many rounds as were shot in the experiment. It still showed that the barrel was wore out well before the one shooting brass jacketed bullets.
http://www.luckygunner.com/labs/bras...el-cased-ammo/

With the cost savings of the steel cased ammo over the brass cased, one can replace the barrel, which as you stated is a wear item anyway.

Yeah, I wonder though, would S&W replace the 5R 8" barrel in my Sport with another 5R 8" barrel, or with one of the 6R 9"? I kind of think they would downgrade it to the latter.

If you look around you can get Brass cased ammo for a price that is very close to steel cased. Not to mention not everyone is skilled enough to replace their barrel. Not sure what that cost would be if you had to pay someone to replace it for you. Replacing the barrel to some is a big deal that many don't want to deal with. To others its not a big thing at all. Just comes down to the individuals choice.

Been shooting pmc xtac 556 55gr & tulammo 223 55gr (steel casing). Shoots fine & no ftf. Just lube your bolt really good & you'll be fine. And always keep proper maintenance on your rifle. The cleaner the better!