.223 vs 5.56 NATO pressure difference discussion

[Bart B.]

That would not have been an example of a tight Palma bore. I had in mind the custom barrels like Krieger's .30 Tight series.

Such as the .3065" groove diameters used with 7.62 NATO M80 ball ammo's .3070" diameter bullets.

Always been fascinating to me that squeezing very uniform bullets down a few to several tenths makes them shoot most accurate. Upsetting them a few tenths bigger to greater groove diameters tends to unbalance them enough to make them shoot less accurate.

 

[Unclenick]

I suspect what happens is the tighter bore does a better job of getting the bullet straightened from any slight tilt it may have, where a loose one more easily leaves the tilt intact and just fattens the bullet behind it more. I'd have to try some experiments with the effects of extrusion on mass symmetry, but I've observed that if you measure case wall runout at the back end of a new .308 case near where the pressure ring will form when it is fired, the neck, which has been extruded narrower than the body, has less wall thickness variation than the pressure ring area does.

 

[Bart B.]

Perfect straight rimless bottleneck cartridges are typically a bit crooked in the chamber and bore when fired. They pivot about the case-chamber shoulder contact and their pressure ring area is a thousandth or so pushed off center against the chamber wall by the extractor. The bullet tip is therefore off center the bore about half that of the pressure ring area in the opposite direction.

No worries as it's very repeatable across all such cartridges.

 

[9MMand223only]

I guess my question about the pressure difference is this.

Why does it matter? My opinion is that SAAMI is awful and is terrible. I view it as misleading. And it is.

Why not just forget about SAAMI/NATO, whatever, and just load a round that accomplishes what you wish it to do? That doesn't blow primers, bulge brass, etc?

 

[Bart B.]

I guess my question about the pressure difference is this.

Why does it matter? My opinion is that SAAMI is awful and is terrible. I view it as misleading. And it is.

Why not just forget about SAAMI/NATO, whatever, and just load a round that accomplishes what you wish it to do? That doesn't blow primers, bulge brass, etc?

Exactly what is misleading?

I've shot proof loads generating about 67,500 cup (82,000 psi) that didn't blow primers nor bulge cases visually different than normal loads. Is that ok by your standards?

 

[Unclenick]

The whole purpose of SAAMI is to allow manufacturers to make ammunition that will work in all working guns chambered for a particular round. If your individual gun is tougher than the weakest ones out there in your caliber, and you are willing to sustain more rapid wear than average, then, by all means, do what you please, understanding that is is at your own risk. Just don't be surprised, if you switch cases or primers, that suddenly signs of a problem appear where there were none before the switch.

 

[9MMand223only]

Exactly what is misleading?

I've shot proof loads generating about 67,500 cup (82,000 psi) that didn't blow primers nor bulge cases visually different than normal loads. Is that ok by your standards?

Bart:

If that load works good, I am perfectly fine with it.

It is misleading because people are fooled into thinking going higher than SAAMI means its default "unsafe". That is a myth. Going too low powder is vastly less safe if you ask me. The only danger I have ever known to reloading, isn't pressure, its impediments inside the barrel (another bullet stuck, etc). That is the danger.

How do you know you did 82,000 PSI? Quickload has many issues. Its wildly inaccurate for many loads. Wildly. It could be what QL told you was 82k, is under 60. Its actually hard to load 82k on purpose in a 223. You would have to use really fast powders and make gross measurement mistakes. So many 223 powders, you cannot fit enough powder in the case to even get near ~65k.

 

[Unclenick]

I expect Bart shot test loads with measured pressure and that QuickLOAD wasn't involved in any way.

"It is misleading because people are fooled into thinking going higher than SAAMI means its default "unsafe".

It's not SAAMI's fault. They are just a group of industry guys who get together and decide where to set the standard for an individual cartridge to be copied so a manufacturer can put ammunition products on the shelf that will work in all guns chambered in that caliber, including yours and guns weaker than yours. SAAMI is not a handloading organization and how people apply their standards to handloading is pretty much the choice of the individual loader or the load manual authors. Here, we require the hot load warning to go in when loads are above published loads for liability reasons. It's not to say you can't experiment further on your own.

 

[Bart B.]

I expect Bart shot test loads with measured pressure and that QuickLOAD wasn't involved in any way.

Yes.

CAUTION: The following post includes loading data beyond or not covered by currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

7.62 NATO M60 proof load equivalents hand loaded by the USN Small Arms Marksmanship Unit in San Diego or my own handloads. Several sites list the IMR4475 charge and bullet weights.