Head space issue?

50 grains of AA 4046 over 165 grain accubond. Set close to the lands and very accurate load. I don't have any pressure sighns exept flattened primers either. There just inst much info on AA 4064 OAL 3.353. Some how I missed Uncle Nicks post asking.
 
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I am with Mehavey.

Your load may be mildly hot - that should not begin to take out top quality brass in 2 firings or less.

AA4064 is close but not over the limit ( 8/10 less) with a 165 Nossler Partition and its 2.3 grains less for an all copper Barnes.
 
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Barring a dramatic Lot# problem.....
and using Default 68gr H2O case capacity:

30-06/165NosAccubond/AA4064/50gr
barely makes 51,000psi in a 60ksi cartridge
+10% BurnRate --> 61,000

w/ Nosler case: 72gr
46,000 psi (+10% BurnRate --> 55,000psi

Barring gross blunder on somebody's/manufacturer's part, the OP isn't even close to overpressure.
Far from it.

JWilson:
- Get yourself a Headspace Comparator
- Size a once-fired case to where the bolt will juuuuuust close on it
- Measure the headspace dimension/subtract 0.002" --> Write It Down
- Size all future cases to that dimension
- Let us know....
:)
 
Mehavey,

You must have missed, way back in his second post, that the OP said his case heads were coming out +0.003" wider in diameter than before firing. That's a very strong pressure sign, which is why I asked about the load and suggested reducing it.

In his description of the load, he says the bullet is very close to the lands. Many people think you actually have to contact the lands to get the pressure increase associated with such contact, but you don't. Dr. Lloyd Brownell's study of pressure in the 60's showed that, beyond a minimus, pressure rises in an s-curve shape that approaches the contact pressure continuously and is almost there just before contact is actually made. This can cause anywhere from about 20% to 30% increase in the pressure rise in some guns and bullet and powder combinations, as compared to having some normal jump, and that's what I suspect happened here. A load that should be 61,000 psi with jump could get up into the proof range, and be 73,000 to 79,000 psi.
 
I made 3 rounds yesterday with 55 grains of imr 4350 reduced the OAL AND I still see the cracks with brand new norma brass although they are less noticable. Accuracy was terrible at 100 yards. Nice rounded Winchester primers.
 
How about the head diameters?

If the primers were rounded, this is starting to sound stranger than expected.

Can you take and post photos of the cracks and the case heads? Before and after, ideally. After cleaning and before resizing, then again after resizing.

Also, you said it's not happening with commercial loads. Something odd is certainly going on here.
 



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Before sizing
top is 50 grains of Aa4064 1st firing norma brass
Second is 55 grains of imr 3540 1st firing norma brass
Third is RP brass 2nd firing 1st firing factory in my rifle second firing 50 frains of AA4064
 
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Assuming that you have measured your chamber and know the distance from the bolt face to the lands, with the bullet seated at 3.341", how far off the lands does that put it??

The reason I am asking is explained in Unclenick's post #49.

Also, you understand that almost all bullets have manufacturing tolerances that create different distances from bullet base to ogive, and seating with an OAL (to the point of the bullet) instead of CBTO (cartridge base to ogive), all your cartridges can have the same OAL but the CBTO can vary as much as 0.005" more or less.

I am stating this as I have learned from experience (normally known as the hard way) that the symptoms you are having CAN be created by seating with too little bullet jump to the lands.

I start load development generally with a 0.020" jump and sometimes 0.030".

The most accurate rifle that I have developed loads for has a 0.204" jump to the lands. that is not a typo. It is a hunting rifle and will put 10 holes into 3/8" consistently.

A 0.003" case head expansion is not a good thing. The case head is not normally supported by the chamber.
 
I used a modified case and a bullet to determine where my lands are and backed off .003 I very well could have made a mistake. Is there a better way or a tool to help determine where the lands are.
 
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