I need load data for the Hornady 224 caliber 55 gr GMX bullet in the 223 Wylde chamber AR15).

The Wylde throat dimentions are between the .223 and 5.56. Start with .223 load data, and stop when you see pressure signs. Hornady uses a true spirepoint design, as opposed to a secant design, as will build pressure faster then teh secant design, so I would suggest reducing your starting point a little extra if you are cross referencing with a secant design such as the nosler BT's.

Thanks A.S.

Well I'm useing 25.0 gr Varget with the Hornady 55 grain GMX. It Puts 5 shots into 5/8" @ 100 yds. No pressure signs in my AR. Wylde chamber Lothar Walther 16" medium weight 1in9 twist SS barrel. Next it to shoot over the chrony & to start bumping up the load .2 grains at a time. Will post the results here.

Thanks for posting your results. Glad you founds such a consistant load.

One of my best in the 5.56 chamber, (1/9 16")is:
25.5gr of IMR 4895
60gr Nosler Partition
CCI BR4 primer
Winchester case.

Shoots groups about like yours.

I also bought some of those Nosler 60 gr partitions. I'll be trying your recipe next.
Thank you!

Your welcome!!

It's a max load, and your throat is tighter then mine, so as always, work up.

Antelope: Can you tell us what a "secant" ogive is, and perhaps why Hornady misrepresents their bullets as having secant ogives when you inform us otherwise?

And can you describe a tangent ogive as well so we'll know the difference.

While you're at it, would you mind briefly outlining the physics of why the Hornady "Spire Point" will "build pressure faster than the secant ogive". This would be fascinating and informative.

Most AR's are over gassed to insure they will function under all conditions. This tends to leave a very flat primer giving the impression that the load is very hot. This is one of the reason David Tubbs came up with the carrier weight to slow the action. A better method is to use an adjustable gas valve. I have a Colt AR15 HBAR. When I first got it many years ago I was loading guaranteed middle of the road loads and the primers came out looking very flat like high pressure. I put an adjustable gas valve on it and with the same exact loads the primers now have normal looking conditions with rounded corners. If I get a high pressure flat looking primer now I know that I am getting in the danger zone for sure.

Stoney, Good catch. I said secant when I should of said tangent.

A standard spitzer, or tangent ogive, is a special case of the secant ogive where the angle of intersection is 180-degrees, or the offset from tangent is zero.
The Hornady Vmax as a good example:


Ok, enough of the gobblie gook. What's important in this picture, it the point where the bullet departs from the full diameter section, and starts to narrow to a point. With this traditional spitzer design, this departure is sharp, and the line from this point to the tip of the bullet is essentially a straight. Now if this line of departure is changed from 180 degrees, it's no longer a standard spiter, and become a secant ogive.

By contrast a Tangent ogive "arcs", like a partial circle, with a specific radius normally stated in calibers.

Lets look at the ballistic tip:



Compared to the vmax, it's easy to see where the point of departure is curved, an not essentially straight.

Their are two practical implications for this when it comes to reloading. The VMAX will have a more sudden engagement with the lands, where the ballistic tips will be more gentle. Consequently, all else being equal, I would expect (and have experienced) higher pressures with the VMAX compared to the ballistic tips. Second this gentle vs sudden engagement with the land make the tanget design less finicky to OAL then the hornady.

Now what we today consider a secant ogive does not include the spiter point. Instead of a short, sharp triangle point like you have on the vmax, they have a loooooong triangle nose. An example of this would be the Amax:




Some bullet makers are now combining the best aspect of both of these designs in what is called a "hybrid designs. They have the long pointy nose of a secant, and the rounded junction of a tangent design, attempting to provide the best of both worlds. Many of us know how Berger bullets can be very sensitive to seating depth. It's for this reason that Berger in now offing some "hybrid" bullets.



Those are the nose shapes in a nutshell.

The hypothesis that the sharper transition from ogive to full diameter of the secant shape as compared to the tangent shape results in higher chamber pressures is a novel theory that I don't think I've seen expressed previously. Perhaps I've simply missed any scholarly research or analyses of this proposed phenomenon. I'd love to read what others have said about this. Can you point me in a direction where I could find additional information?

I realize that there has long been a presumption that greater bearing surface results in greater pressure (all other things being equal), but this theory seems independent of bearing surface since there is nothing about the ogive shape itself which necessarily impacts on the length of the bearing surface.

Stoney, I haven't seen anything printed on the subject, it's something I've observed through chronographing, and finding maximum pressures.

You are correct that nose shape can affect bearing surface, but I've observed this phenomina in bullets with very similar vearing surfaces. But in that regard, when I get a chance, I think I will pull out my caliper and see if those bearing surfaces are as close as I believe.

But. Since the tangent ogive bullet will have to be seated DEEPER into the case than the secant ogive bullet when both are seated the same distance from the rifling means that the chamber psi will increase due to having to seat the tangent deeper. They might cancel each other out.

On a long secant that maybe the case. You would have to test to see. But when comparing the Vmax to the BT, in an AR, a safe load with a 55gr BT can blow primers with a 55gr Vmax.

quote:

But when comparing the Vmax to the BT, in an AR, a safe load with a 55gr BT can blow primers with a 55gr Vmax.

Agreed!