Do AR-15 Heavy .224 Bullets Need To Be Single Shot?

[skydiver]

Hey There,

I once read somewhere that with heavy .224 bullets, that you need to shoot them single fire in an AR-15.

The reason is that they won't fit or feed reliably from a magazine because they are too long.

Is that true and if it is what grain weight does it apply to?

Thanks for your help!

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[Nwcid]

It refers to any that have an OAL length longer then the mag. If you are buying loaded ammo it should say if it will fit or not. I am not aware of anyone selling loaded ammo that will not fit.

If you are hand loading then you will just have to see what length the bullet you buy are. If you are shooting that heavy of a bullet you will also need a fast twist barrel because of the bullet lenght.

 

[HollisOR]

All box magazine firearms have a problem with case length. If they are reloads, they need to be seated deeper. Also powder level checked before doing that. Refer to a reloading manual on loads. If they are not reloads then, to shoot them, they need to be singled feed. Not all .223 Rifles are the same. People who reload for highly accurate rounds will set their bullets to be within/about 0.015 off of the lands/groves in the barrel. That can make for a long case length. In fact too long for the magazine.

 

[skydiver]

I have a 1/7 groove barrel.
I am planning on reloading myself, but didn't know if a certain bullet weight becomes too long.
In other words, what is the heaviest .224 bullet I can load and still work reliably from a magazine?

 

[Nwcid]

It will depend on the brand and the length. Each brand and style is different so it is not that easy to say. Basically if you are getting into the high 70's gr I would be doing some measuring. Assuming you are using load data from a book or an online source simply see what the listed OAL of the loaded round is and see if it fits.

 

[deadshot2]

If you do reload longer bullets don't overlook HollisOR's last comments. The OAL shouldn't be so long as to put the bullet INTO the lands but back by .015"-.020".

If you go TOO long and jamb the bullet into the lands you run a couple of risks. One is that the bolt won't go fully into battery. The other is that the case pressures could be too high for safety.

A healthy dose of Caution and doing your research is in order.

 

[Grommit327]

Generally 77g SMK's are good to go for a 2.260 OAL (Max AR mag length) but the 80 and 90 grainers can't be seated that deep. And {gasp} I actually have heard that people can get the 77's to stabilize out of a 1-9 twist barrel. According to the internetz people there's no way that can be true.

I've been running 69's out of my 1-8 twist barrel and about ready to step up to 77's and see if I can get a load worked up.

 

[Gunner3456]

You have a maximum overall length for any round for your gun. If the bullet is longer, you seat it deeper to get that overall length. If there is too much powder to do that, you need to switch to a different powder that takes up less space.

I haven't loaded that length of bullet, but someone on here surely knows a good powder for that load.

 

[deadshot2]

. And {gasp} I actually have heard that people can get the 77's to stabilize out of a 1-9 twist barrel. According to the internetz people there's no way that can be true.

[chuckle]and to think I can get a 220 gr bullet to stabilize and be extremely accurate from a barrel with a 1:10 twist rate. Go figure.[/chuckle]

It's amazing how "stupid" we all were before the Internet

 

[Gunner3456]

[chuckle]and to think I can get a 220 gr bullet to stabilize and be extremely accurate from a barrel with a 1:10 twist rate.

Not in .224 caliber you can't.

"This is the internet speaking, LOL"

 

[Capn Jack]

A .224 dia. 220gr bullet :huh: Hmmmm.
I wrap those around my line for Steelies.

Jack...

 

[HollisOR]

A .224 dia. 220gr bullet :huh: Hmmmm.
I wrap those around my line for Steelies.

Jack...

Those are made with depleted uranium.

He is probably talking about a .338 rifle with a 1:10 twist.

 

[Gunner3456]

A .224 dia. 220gr bullet :huh: Hmmmm.
I wrap those around my line for Steelies.

Jack...

.224 220 grain? That's what I use for a fishing pole, LOL.

 

[deadshot2]

Not in .224 caliber you can't.

"This is the internet speaking, LOL"

Where did I say .224???

They are actually .308's shot through my 1903.

You'd be amazed at the number of people who think I need a "faster twist" after reading all the hype on the AR Forums.

I use this "calculator" to see what bullet and speed works best for my barrels

http://kwk.us/twist.html

There's no entry for "Weight", just length, diameter, and speed.

 

[Gunner3456]

Where did I say .224???

There's no entry for "Weight", just length, diameter, and speed.

I guess you didn't. The twist rate needed is about aspect ratio regardless of caliber. That's why you need to know only the ratio of length to thickness of the bullet. Obviously in a given caliber, the heavier bullet will be longer, giving it a higher aspect ratio and therefore a need for a faster twist, but you're right, all you need to know is caliber, speed and length.

 

[deadshot2]

I guess you didn't. The twist rate needed is about aspect ratio regardless of caliber. That's why you need to know only the ratio of length to thickness of the bullet. Obviously in a given caliber, the heavier bullet will be longer, giving it a higher aspect ratio and therefore a need for a faster twist, but you're right, all you need to know is caliber, speed and length.

But if you take that same bullet and send it down range faster it will stabilize with a "slower" twist rate. Also, some bullets are longer without necessarily being heavier, ie solid bullets made from copper/brass.

 

[civilian75]

It is about center of mass location and rotational moment of inertia. The "caliber, speed and ratio" formula works most of the time but sometimes it fails to explain why, for instance, a 1:10 ratio may barely stabilize a 308 caliber 220gr FMJBT with a secant ojive but won't stabilize a shorter round nose soft point 220 gr. The latter center of mass is located farther back than in the former. The farther back the center of mass, the more unstable the bullets are. I downloaded a couple of years ago a program that took bullet geometry and material composition into account and was a bit better at predicting stability. Unfortunately, I haven't been able to use it since I upgraded to Win 7. This is were I got it from:Ballistic Software - JMK's Home Page

In summary, the "caliber, speed and ratio" formula is a simplification of a more complex physics problem may not always work, so keep that in mind.

Skydiver, sorry for hijacking you post.

 

[Gunner3456]

But if you take that same bullet and send it down range faster it will stabilize with a "slower" twist rate. Also, some bullets are longer without necessarily being heavier, ie solid bullets made from copper/brass.

Sure. Tracers are very long but lightweight. They still need a fast twist (1:7 in an AR-15) because of their length, not their weight. In fact, it was the tracers which prompted the military to go to 1:7 twist, and then swap from 55 gr to 62 gr so the bullets would work with the faster twist.

 

[Gunner3456]

In summary, the "caliber, speed and ratio" formula is a simplification of a more complex physics problem may not always work, so keep that in mind.

Yep, it's about cross sectional density, aspect ratio, and ballistics coefficient if you want to get technical. Still, in the same style of bullet, the heavier one will be longer and will require a faster twist within a certain range of twists. By that, you can shoot different lengths in a certain range of twists and be OK, such as shooting the 55 gr or 62 gr in a 1:9 twist AR, or the 62 gr but not the 55 gr in a 1:7 twist.

 

[deadshot2]

The farther back the center of mass, the more unstable the bullets are.

Yet the choice of bullets for precision shooting is almost always a bullet with a center of mass purposely moved back by by making it a hollow point. Match bullets have no requirement in the traditional sense, expansion in game animals, it's done to enhance their stability. Go figure.