Hey everyone!
Quick question here. I recently picked up a sport (my first dip into the AR pool) and I love it.
But I have noticed that I get a much better grouping at 50 yds with .223 ammo than I get with 5.56 ammo.
Any rhyme or reason to this? Anyone else notice this?
Maybe its just me.

NATO ammunitions are generally constructed to to meet a specific Energy Level requirement with accuracy a secondary concern. One result of this approach is ammunition loaded near the maximum pressure levels instead of a pressure level that optimizes accuracy.

The .223 Remington ammunitions are quite often Varmint or Hunting loads where accuracy is a critical consideration. In addition the .223 R also features a lower maximum pressure than the 5.56 and it's been my experience that loads built "hot" generally aren't nearly as accurate as loads running just 100 fps slower.

So, IMO what you are seeing is to be expected to some extent. As a Reloader I've found out first hand that my most accurate loads are somewhat "sedate" for these calibers. For example one sub 1/2 MOA load I've worked up using a 60 Grain Nosler Ballistic tip Varmint bullet only clocks 2950 fps from my 20 inch Shilen barreled precision AR. I can also tell you as a reloader that you just can't build accurate ammunition using bullets produced for Military ammunition by the Lowest Bidder for that item. Finally, I can also tell you that it's also been my experience sometimes loads will do things that just make you scratch your head. For example that Nosler bullet works wonderfully with Varget powder but with CFE223 powder I have not been able to get it under 2 MOA at any listed charge weight.

PS; while I've built every one of my AR's and don't own an M&P 15 Sport every time I see one for sale at 600 dollars I cannot but be tempted by that package. To put it simply, you've purchased a heck of a good bargain rifle.

Good reply scooter,you nailed it.

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Hue 68 noli me tangere

Varget starting load 23gr V-Max 55gr bullets will give me 1/2 to 3/4 inch groups at 100 yards. I could not fine a CFE load that will do better then 1". , but then Anerican Eagle ammo would only do 2 to 3 in groups. I just build a lower this week that has a National match trigger and put my MP15 MOE upper on it. Went to the indoor range today to try it. Put three bullets through the same hole at 20yds with the Varget loads.

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USN Retired/VN VET
M&P X5

I get the opposite, my Sport loves XM193 and is slightly, trivially, less accurate with AE 223 or PMC 223. I still mostly shoot 223, though, due to cost and slightly lighter recoil for range work.

Thanks for the replies and thanks for the in depth explanation, Scooter.
I was just now wondering if it had anything to do with the 1/9 barrel twist. Will the pressure of the .556 have an effect on that?

Not to an extent that you can attribute your accuracy to. Higher pressure giving less consistent velocities, military bulk 5.56 isn't going to be the most accurate out of any rifle.

Bullet quality is to me, the most important indicator of accuracy.

A 55 gr. V-Max, or Nosler Ballistic Tip, will usually out shoot the military FMJ loads.

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NRA Instructor

Don't barrel harmonics come into play here? And if so - don't they also vary from gun to gun?.....meaning Sport #1 may shoot a given 5.56 load better than a given .223 load, but Sport #2 may be the opposite.

My question -- if you have noticed one doing better than the other, how many different loads of each have you tried? If the answer is only one or two, then all you really know is that a specific load of A will outshoot a specific load of B. The next pair of loads may give exactly the opposite results.

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Pisgah

This is true. I have only shot one type of 5.56 so far. it was american eagle brand. And Ive only shot 2 different types of .223. I'll try more and see if it does indeed change.
Thanks

If you dont mind steel case and run across any 62 gr Wolf FMJ, give it a try. 1/9 twist barrels do very well with a heavier projectile.
I was very pleased with the 62 gr bullets accuracy in my Sport. Mine barrel is 1/8 5r but My 1/9 loves them too.
Good Luck
Jim

No two guns are alike and you need to try several loads to find one that does well in YOUR gun. My MP15 shoots the ZQI 556 62g (SS109) very well.

Better than the AE 223 55g I've shot.

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_It was love at first shot_

you said you are tempted to buy a Sport when it goes under $600. try this website. gunwatcher.com. I have seen it dip below $500 with NO shipping.