I own an MP-15 chambered in .223. I was wondering if I can convert it to .224 myself. If I can, how would I go about doing so?
~LiberalTears

You're already firing a .224 diameter bullet, so no mods are necessary. If you meant 224 Valkyrie, then a whole new complete upper plus mags would be needed.

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Peace was my Profession

.223 Remington, also known as 5.56 x 45 mm in military guise, is actually firing a projectile with a 0.224 diameter.

You should already find abundant stocks of .223 Remington or 5.56x45 ammunition (both should be treated as interchangeable as your rifle is chambered for 5.56).

If you are asking this question because you are considering getting into reloading, then please note that this question indicates your need to obtain and study at least one, possibly two or three reloading manuals and then read - no, study - the section at the front on "How to Reload".

Are you talking about .224Valkyrie?

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Freedom isn't free.

I don't know if the mp-15 is available chambered in both .223 and 5.56, but these rounds are not interchangable.

A rifle chambered in .223 with a tight chamber will lose accuracy and reliability shooting 5.56. A rifle chambered in 5.56 will shoot both,although I don't know how accuracy is affected.

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This is the internet myth and is wrong.

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And yet strangely my AR chambered in .223 becomes a single shot and 100 yard groups go from less than an inch to over 6 inches when using 5.56.

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What AR do you have that is chambered in .223?

I'd get a kit to get the headspaced bolt / barrel combo. You just need the barrel and bolt everything else beside mags is the same.
You'll also need 6.8SPC type mags for best reliability.

PSA 20" Rifle-Length .224 Valkyrie 1/7 Stainless Steel Barrel & BCG Combo - 5165447820

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Straight shootin'
SWCA#2439

Before i knew what I know now I had a guy build me one with a long heavy barrel for varmint hunting.He asked me if I wanted 5.56 or .223 since his preferred barrel choice for quality/price had both ( ER Shaw ).

Since then I have built another upper chambered in 5.56 to get a little more use out of the gun just shooting at the range..

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OK, if you have a precision made .223Rem chamber then I could see a difference. The shoulder of the 5.56x45 is slightly different. In a precision made chamber it could cause accuracy issues. Going from <1MOA to >6MOA seems extreme, but all guns are different. Most will not have issues like that. Maybe your chamber is tighter/looser than normal?

Also, turning into a single shot is weird. The chamber shouldn't affect that at all unless the cartridge is getting stuck. Or the chamber is so loose that a bunch of the gas is escaping past the casing as it's fired. That doesn't seem possible because the 60,000psi would just expand the brass enough to seal it up.

I don't know. You're the first I've ever heard of to have this issue.

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Freedom isn't free.

Yeah, the cartridge is getting stuck...I usually have to tap it out with a cleaning rod. It isn't an every shot thing, maybe half the time or a little more ? But between the reliability issues and the accuracy I just stick with .223 for that upper. The 5.56 upper doesn't seem to care either way,although I haven't shot much .223 out of it to see how it effects accuracy.

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There are some minor differences in chamber dimensions between .223 and 5.56 mm. The major change is in freebore and leade (sometimes called throat) angle. The 5.56 mm chamber has a longer freebore and a more gentle angle on the leade.

If you had a tight chambered .223 and fired 5.56 mm in it, you might see some signs of excessive pressure if the 5.56 was actually loaded to max average pressure. You should see signs of that on the primer. I've got a minimum chamber .223 bolt gun that shows no signs of excessive pressure (relative to the same ammo fired in a 5.56 mm chamber) with 5.56 mm ball.

If your functionality is right on the ragged edge, the extra extraction effort might cause the problem you're having. I'd suggest installing a new correct extractor, extractor spring and insert. Possibly add a D ring to the extractor. Then try again.

The only thing I can think of off the top of my head that might cause your change of group size would be rifling twist that doesn't match up with your 5.56 mm ammo. Or some massively out of spec ammo.

Thanks for the input, but honestly not worth it to me. The upper chambered in .223 feeds,fires, and ejects fine with .223. Only when I go to 5.56 do I have issues. So I'll just stick to the .223 ammo for that upper.

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