I used to think they were the same cartridge, but now I see that the 5.6mm develops more pressure. My question is which seems to be the better choice for the AR15 Sport? [Current production with 1/8 twist.]

Either will work fine. You will probably find more choice in projectile in off the shelf loads for .223 than you will 5.56mm.

Cyphertext is right. .223 Remington or 5.56 NATO will reliably function in your rifle.

If you gave us some additional information as to what type of shooting you're doing, it would be helpful.

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-John

Current production is 1:9 twist...

If the guy says his barrel is stamped 1:8, then that's all I can go by. There is a chance that he bought new old stock. If that's the case, then jackpot!

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-John

Six of one, half a dozen of another. Bullet weight will probably effect accuracy more than the difference between 5.56 and .223 in a Sport.

Historically, .223 is generally the more accurate cartridge, but there are many variables to be considered.

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SFC, US Army, Retired

I kinda freaked out after I bought my Sporter, thinking I could only shoot .223. Then I saw the 5.56 stamped on the barrel (I know, reading some dub****s posts on some random sight and not knowing my own weap...) Anyway, I've shot steel case 5.56 and .223 (use lots of lube) penitrator 5.56, American Ammo .223, it all shoots. I just got a bunch of 5.56 ball M193. As for me, I plan on using the .223 for re-familiarization and plinking and target shooting out to 300 yds because it's cheaper. I plan on using the 5.56 M855 and M193 at longer ranges with a scope to see just how far I can push the limits (My range just built out to 600 yards) and see if there really is a huge difference between 62 and 55 grain. I've always trained as a CQB team member, so like what JaPes said, it really depends on what you want to be doing with it. CTDirt had really good prices on CBC Ball M193, so I bought enough to get me through the season. If .223 had been as available I probably would have bought that. Just buy as much reliable ammo as you can and get at it while the prices are down.

Nato ammo normally more expensive without any noticeable advantage to my shooting, so I shot .223 fine. Tulammo is great, I don't pickup bronze after shooting as well so no point in it.

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