223 - max bullet weight for 1:9 twist

[DubiousDan]

What is the maximum bullet weight for 223/5.56 that will be stable with a 1:9 twist barrel?

 

[Charlie]

I've had good success shooting 69 gr. and 75 gr. from my AR with a 1:9. The problem I run into with heavier (and most of the time longer) bullets is being able to hold to a correct cartridge overall length and still trying to fit them in a magazine. If you're shooting from a bolt action this, of course, would not apply.

 

[Mikewood]

Yep. The 1-9 is good for just about everything. You chose well!

 

[shortround]

I assume at 100+ yards/meters?

1-9 will surely stabilize the Sierra 69 grain HPBT-Match, the Nosler 69 grain HPBT, and Hornady 68 grain BTHP Match.

It may or may not stabilize the Hornady 75 grain BT A-MAX, which calls for a twist rate of 1-8.

OTOH, lighter bullets under 62 grains might give erratic performance, and the lighter ones will tend to disintegrate before reaching the target.

Be well.

 

[Texas42]

What is the maximum bullet weight for 223/5.56 that will be stable with a 1:9 twist barrel?

Not every 1/9 twist barrel is the same (might be a 1/9.5 or 1/8.7), a the only way to really know if your barrel will handle the upper limit of normal is to shoot it.

What are you looking as shooting?

 

[DubiousDan]

Not every 1/9 twist barrel is the same (might be a 1/9.5 or 1/8.7), a the only way to really know if your barrel will handle the upper limit of normal is to shoot it.

What are you looking as shooting?

I'm shooting an AR and it's mostly for fun. I've been shooting 55gr and they do OK but I'd like to try a heavier bullet with the thought of possibly using it for hunting. The rifle is a DPMS Panther and the paperwork says it's 1:9.

 

[M. Sage]

OTOH, lighter bullets under 62 grains might give erratic performance, and the lighter ones will tend to disintegrate before reaching the target.

Be well.

In a 1:9? You're good down to around 40 grains in a 1:9. It's the 1:7 barrels that tend to turn light varmint bullets into confetti.

 

[Bultx1215]

I've gone as low as 50's with my 1:9 and as high as 70g. They all work well.

 

[Texas42]

Just be careful with copper rounds, like Barnes TSX (a premium, quality hunting bullet I've used). Copper is lighter, and hence the rounds are longer than their lead equivents. Which is why they recommend a 1 in 8 twist for a 70 grain TSX. Many of the bullets mention what kind of twist they recommend (for reloaders anyway).

 

[M. Sage]

Just be careful with copper rounds, like Barnes TSX (a premium, quality hunting bullet I've used). Copper is lighter, and hence the rounds are longer than their lead equivents. Which is why they recommend a 1 in 8 twist for a 70 grain TSX. Many of the bullets mention what kind of twist they recommend (for reloaders anyway).

Heh, I was just coming back in to point out that the bullet length plays more a role than weight. Though bullets with similar materials and construction will be longer when they're heavier. 1:7 came into military use to stabilize the very long (but not actually heavier than normal) long range tracers.

 

[JimBobKelley]

Wish I could take credit for this but I found this on another forum. You may find some use out of it. Like others have said, try it and see what your rifle likes.

This is my guide for twist rate for any caliber
It's a short version of the Greenhill Formula
OLD but it will get you close.
Formula for bullet velocities UNDER 2800 fps
150 X bullet diameter squared divided by bullet lenght
Formula for bullet velocitis OVER 2800 fps
180 X bullet diameter squared divided by bullet lenght
So lets try a .243 Winchester for example, at under 2800 fps
.243x.243= .059 bullet diameter squared
150 x .059 = 8.850 divided by the lenght of the bullet I picked a .750" long bullet
8.850 divided by .750 = 11.8 or a 1 in 12 twist

 

[Texasjack]

I don't know why this caught my eye tonight, but it gave me the chance to do a little research. For one thing, I've always wondered why .223 barrels weren't all 1:7. I found some retired engineer (who used to design nukes) that did a calc on how fast a copper jacketed lead bullet could spin without coming apart. Turns out that at a twist rate of 1:7, the velocity limit is 2989 fps. (1:8 = 3416, 1:9 = 3843, 1:10 = 4270, 1:11 = 5124)

You can calculate the best rate of twist for a particular bullet using the Greenhill formula, which is T=CD[SUP]2[/SUP]/L
where C= 150 (up to 2800 fps; above that use 180), D= bullet diam., L= bullet length. For a .223, you could use 8.95/L.

According to Shilen (and others) a twist of 14 is good up to 55 gr, 12 for 40 gr to 63 gr, 9 up to 70 gr, and 7 or 8 for 70+ gr.

 

[Texasjack]

Check this chart: .223 Rifle Twist Chart

 

[M. Sage]

I don't know why this caught my eye tonight, but it gave me the chance to do a little research. For one thing, I've always wondered why .223 barrels weren't all 1:7. I found some retired engineer (who used to design nukes) that did a calc on how fast a copper jacketed lead bullet could spin without coming apart. Turns out that at a twist rate of 1:7, the velocity limit is 2989 fps. (1:8 = 3416, 1:9 = 3843, 1:10 = 4270, 1:11 = 5124)

He's wrong. The spec for M855 is 3100 ft/second, and that's being shot out of 1:7 barrels all the time. Construction of the bullet plays a large factor. Thinner-jacketed varmint bullets shot through a 1:7 barrel can come apart, but heavier-jacketed bullets in the same weight and same velocity will survive the trip to the target. I've shot 55 grain bullets out of 1:7 barrels, and never had them fail. Accuracy might not be as good as it should be, but they all make it to the target in one piece. Mil spec for M193 (the old 55 grain load) is 3250 fps, and I've seen plenty of that survive shooting in 1:7 rifles.

Going 1:7 gives you the option to run longer/heavier bullets, and will be less accurate with lighter bullets. Will some of them fail? Yes, but usually just the very light, thinner jacketed varmint bullets.

Different bullet designs have different jacket thickness. Target bullets tend to be thinner, varmint bullets tend to be very thin, hunting bullets and military-style FMJ tend to be thicker.

 

[Texas1911]

Well ... a 1:7 barrel isn't always a "true" 1:7 either. Bullet construction plays a big part in how they stay together, and I've seen more than my fair share of bullets come apart outside the barrel. Stuff like 62 grain ball, 40 grain VMAX, etc. predominantly out of the 20" 1:7 barrels, although I've seen 14.5" to 16" CAR barrels spin em up fast enough to come apart.

 

[M. Sage]

What kind of 62 grain ball are you seeing come apart in 1:7 barrels? The military is using 62 grain and the muzzle velocity I listed is the military spec for muzzle velocity for that load (M855).

It comes down to construction. Vmax is one of those thin-skinned varmint bullets...

 

[Charlie]

You guys beat me to it. Stability of bullets has to do with length, not weight. And of course the heavier the longer (usually) and material const. does play in the scheme of things also.