Why more powder for 223 than 556

[triggerjerk]

Hornady 62gr website download data shows more powder in 223 for 2230 and xbr than for 556 and equal max loads for TAC. Emailed em and they simply said lab said that where pressure got high.

Would someone explain to this fudd how that works? Did I just get complacent and not notice that 556 doesn't always have more powder than 223 at max? Below are powders listed in common:

556
AR-Comp 17.6 gr.-24.6 gr.
H322 20.0 gr.-23.3 gr.
Accurate 2230 20.5 gr.-23.6 gr.
H335 21.2 gr.-25.4 gr.
IMR 8208 XBR 21.8 gr.-24.4 gr.
TAC 21.4 gr.-24.7 gr.
NORMA 201 21.9 gr.-25.6 gr.
Power Pro Varmint 22.9 gr.-26.9 gr.
WIN 748 22.5 gr.-25.7 gr.
CFE 223 23.5 gr.-27.7 gr.
BL-C(2) 23.6 gr.-27.9 gr.

223:
H335 20.1 gr.-22.9 gr.
H322 20.7 gr.-23.1 gr.
Accurate 2230 21.3 gr.-24.8 gr.
TAC 21.6 gr.-24.7 gr.
AR-Comp 22.2 gr.-23.4 gr.
WIN 748 22.1 gr.-25.5 gr.
NORMA 201 22.8 gr.-24.2 gr.
IMR 8208 XBR 23.0 gr.-25.3 gr.
Power Pro Varmint 23.6 gr.-26.1 gr.
BL-C(2) 23.1 gr.-27.7 gr.
CFE 223 24.5 gr.-27.4 gr.

Thanks and best to all in these trying times.

Edit: Accurate lists same max weights as Hornady for 2230, but the higher weight is 556 and the lower is 223....

[mRad]

I believe this is because they are referencing a .223 Bolt-action and not a .223 Rem AR. Bolt rifles can take significantly more pressure than ARs.

Also, it may have something to do with lawyers


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[T2C]

A quote from the Hornady Reloading Manual 9th Edition - "The main differences between the 5.56 NATO and .223 Remington is the operating pressure and chamber throat. SAAMI (Sporting Arms and Ammunition Manufacturers Institute) maximum pressure for the .223 Remington is 55,000 PSI. The 5.56 NATO is loaded to 60,000 PSI. Chamber throat for the .223 Remington is shorter than 5.56 NATO chambers as well."

Military 5.56 mm cases are thicker than .223 Rem. commercial cases, which may also play a role in the difference in listed data.

[mRad]

If you compare 5.56 data from Sierra vs .223, it seems the opposite if I remember correctly.


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[DG23]

Hornady 62gr website download data shows more powder in 223 for 2230 and xbr than for 556 and equal max loads for TAC. Emailed em and they simply said lab said that where pressure got high.

Would someone explain to this fudd how that works? Did I just get complacent and not notice that 556 doesn't always have more powder than 223 at max? Below are powders listed in common:

Most likely a misprint.

But... Really depends on the actual chamber. Just being marked a particular way only tells you so much.

Just because you have max 5.56 loads that fire fine in one 5.56 marked barrel does not mean they will be fine in a 5.56 marked barrel manufactured by someone else.

Same with respect to .223 chambers. They are not all the same.


FWIW - Best accuracy does not always come from the hottest round you can send downrange.

[markm]

Military 5.56 mm cases are thicker than .223 Rem. commercial cases, which may also play a role in the difference in listed data.

No they aren't. Most mil brass and commercial weigh the same. (7.62 is a different story.)

[triggerjerk]

I want to say misprint, and hoped they'd fess up, but who am i?

I do try to load for accuracy. Helps at range if accuracy at higher vel, but I don't try to beat conditions with vel.

It's just nice to have a reasonably close and agreed upon max to work up to in the search.

[T2C]

No they aren't. Most mil brass and commercial weigh the same. (7.62 is a different story.)

The walls at the case mouth of my Lake City 5.56 cases are 0.0015 thicker than my commercial Winchester cases. Federal .223 cases tend to be thicker than most commercial cases, but the brass is much softer and they are not suitable for comparison to military cases.

I've cut cases in two with a band saw and observed the web on military cases thicker than commercial cases I cut in two.

What cases are you comparing to Lake City 5.56 mm cases?

[T2C]

I want to say misprint, and hoped they'd fess up, but who am i?

I do try to load for accuracy. Helps at range if accuracy at higher vel, but I don't try to beat conditions with vel.

It's just nice to have a reasonably close and agreed upon max to work up to in the search.

Something to consider is that the leade (free bore) makes a difference in chamber pressure spike and how quickly pressure spikes with a given load. That may account for the difference in chamber pressures when Hornady tests loads in their laboratory and their recommendations for maximum charge weights.

[DG23]

The walls at the case mouth of my Lake City 5.56 cases are 0.0015 thicker than my commercial Winchester cases. Federal .223 cases tend to be thicker than most commercial cases, but the brass is much softer and they are not suitable for comparison to military cases.

I've cut cases in two with a band saw and observed the web on military cases thicker than commercial cases I cut in two.

What cases are you comparing to Lake City 5.56 mm cases?

There is a water capacity chart floating around somewhere where about ten or so different cases were tested / compared. Will try to dig it up and post it...

ETA:

http://i2.photobucket.com/albums/y17...iesresized.jpg