I recently purchased an M&P 15 sport rifle that is chambered in .556 but found that it can't fire any of it straight. I have tried every grain under the sun but get the same results every time. Bullets would impact the target completely sideways whether you fire from 10 feet to 70 yards, so they tumble right when they leave the muzzle. When i took it to the shop they said that the muzzle brake was not "correctly drilled" so i dropped $80 on a new one. Still has the same problem. What should i do to fix this? I havent even put 250 rounds through it yet. .223 shoots completely straight.

Send it back to S&W.

Waiting to see others replies. To me, this does not make sense.....

Larry

Agreed. Since there is only slight differences between the 5.56 and 223, there should be no difference in stability. If it was with both, I could see an issue with the rifling/muzzle crown.

Was this a new rifle, or used? Your post seems to indicate it was used, as it reports that the brake was bad.

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Peace was my Profession

If you're getting non-round holes in paper I think that points quite clearly to a gun problem......which means calling S&W.....which means I'd guess strongly they'll have you send it back and they'll make it right.

Typically you see keyholing when a barrel is warn out.

Not right rate of twist for your bullet weight?

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Len

Have you checked to see if the barrel is rifled? Wouldn't be the first one to slip by various manufacturers.

Could you post a pic of your rifle, if its been too modified than S&W might not be able to help.

If you bought it used we might be able to help narrow down the issue a little better.

What twist is the barrel and when you say every grain there is could you be more specific what you have tried and what brand rds?

Tumbling is a sign of insufficient twist rate or something seriously wrong with your barrel.

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M&P15 sport II, Retired Army

No S&W firearm of any kind, (pistol, rifle, whatever) should send out bullets that keyhole. Send it back and let the experts make it right. Your money matters, they will make it right. Just let us know WHAT the problem was.

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Webfarmer

Strange that it shoots .223 just fine... would expect both to tumble if one does.

There's a few things in the OP that seem strange. Like the "drilled" muzzle brake? The rifle may have some mods.

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Si vis pacem para bellum.

Why do newcomers to these forums post a question and then refuse to answer any requests for a follow up? Kind of hard to diagnose most questions about malfunctions without the proper information.

I suspect the "drilled muzzle brake" was the gun shop picking up some quick profit. An A2 birdcage should cost about $10. A good share of dedicated muzzle brakes will cost less than $80.

Personally, info given by the OP just doesn't make sense. 223 and 5.56 are so close spec wise that what is posted shouldn't happen. Think maybe

https://tse2.mm.bing.net/th?id=OIP.Z...QCcEs&pid=15.1

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Peace was my Profession

Considering it was his first post, with little technical information, I consider his post suspect.......

5.56 rounds are keyholing at ten feet,
and .223 "shoot straight".

Hmmmm...

Did the marathon guy get a new nick?

And no answers to follow up questions ...

Somebody be trolling

I really don't believe that in 10' we would see a keyhole. Tried every grain bullet? Doubt it.

it would take just a couple of thousands of a second to travel 10 feet at .556 bullet speed of near 3000 fps..

would there even be time for the bullet to turn sideways at 10 feet ??

Will .556/.223 chamber in a 6.5, 6.8 or 300 Blackout barrel?

A 300BO chamber should have a shoulder that won't let 223/5.56 ammo chamber! The other two should swallow the round.

I'm putting money on either internet lore or trolling, and I betting there is a bridge short its troll nearby!

Ivan

Maye the bullets in the .556 ammo were loaded backwards into the brass...

: )

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My sgntr is mor thn 30 chrctrs

Took the rifle down to curts guns in milwaulkie. There was nobody down there that could find the problem with the barrel. Instead I put an entirely new one on the gun with a 1/7 twist instead of shipping it off to Smith & Wesson. There seems to be no damage to the old barrel and I am the original owner. No modifications were made to the weapon. Now with the new barrel from another company she shoots straight as an arrow with the same ammunition. There are still no known defects in the barrel from head to toe. It just could not fire 55g, 62g, 77g, or 85g .556 ammunition. This must be a one in a million case. Now the old barrel is just a backup.

You bought a new S&W M&P 15 Sport that you determined had a problem out of the box shooting .556 properly. You took it to a gun shop and had a part replaced (muzzle brake). The gun still wouldn't shoot .556 properly. So then you took the gun to a different gun shop and had the barrel replaced, which resolved the problem.
You have to excuse my lack of understanding, but why wouldn't you have contacted the manufacturer's warranty support and asked to return the rifle to be repaired? Or at minimum contacted the store/website that sold you the gun and asked how to handle the issue (which would have been to call S&W)?
Perhaps you just have a great deal of money and prefer to throw additional money at the problem instead.
Sorry, your story just doesn't make sense.

Glad it's fixed and shooting straight for you, with the old barrel being a 1-9 twist some of those heavier grains might have been a little much.

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M&P15 sport II, Retired Army