light load, loosing primers

mjsdwash · Jun 29, 2018

To anyone who reloads, I have a weird issue. Im shooting a 300aac, 16Voodoo barrel 1/12 twist, and having primers get loose. Brass is mostly Lakecity 2017, or IWI. Loads have been 15 grains of 2400 (published by Nosler), and 17 grains of H110, Vmax110 grain bullets, or RMR 110RN (30 carbine. Not sure what the OAL is at the moment, but the bullet is seated about halfway in the neck, and are not touching the rifling. Bolt is new, barrel has 500 rounds, Headspace is good, primers show no signs of pressure, brass does not need trimming, no wiping on the case, cases land about 6 feet away. It gives no signs of pressure, but a few cases have had primers come loose after 2-3 loadings. Some other cases are on their 5th and have no issues. I use these same cases for 5.56, and know how to remove a primer crimp. I have about 40,000 rounds of .556 on my press, and have never popped a primer, but have now had three in 300aac. After loosing the primers, the holes are enlarged and will not hold a new primer. Worth noting, two of the three popped primers were using the 2400, a powder that is not considered problematic with light loads. Any suggestions appreciated! I'll add for those not familiar with 300aac, these are near starting loads. I worked up to them from starting loads, but as mentioned earlier, no signs of pressure until the primers. Both loads are well below max, and only a little above starting.

Walkalong · Jun 29, 2018

Interesting, 14.5 Grs of 2400 and pulled 147 Gr FMJ gave me a little shy of 1850 ish FPS and no issues. Haven't tried it with the 110 VMax. 30 Carbine bullets (Had some leftover from years ago) were problematic feeding. Was it the carbine bullets load that popped primers? Setback perhaps?

243winxb · Jun 29, 2018

Loaded round neck diameter should not be larger then .334" Whats yours?

ArchAngelCD · Jun 30, 2018

Is it all one brass head stamp that is going loose? I ask because you said some brass has 5 reloads with no problems.

243winxb · Jun 30, 2018

mjsdwash said:
Brass is mostly Lakecity 2017, or IWI.

I see no IWI? http://www.cartridgecollectors.org/headstampcodes?page=headstampcodes#I

If a fat neck gets jammed into the chamber pressure will go up. But there should be other pressure signs.

One of the pressure signs is # 3. The pocket expands a small amount at each firing.

Walkalong · Jun 30, 2018

243winxb said:
Loaded round neck diameter should not be larger then .334" Whats yours?

This is a good one to check considering it is 300 BLK and converted LC cases.

243winxb · Jun 30, 2018

mjsdwash said:
Vmax110 grain bullets, or RMR 110RN

The RMR 110 may make very different pressures then the Vmax?

Testing needs to show what combination of components produce the expanded primer pockers.

mjsdwash · Jun 30, 2018

lots of answers, first, popped primers with both bullets. definitely no bullet set back, i can put enough weight on them to dent some hardwood with no measurable setback, I have a .306 expander. For anyone wondering, the RMR 30M1C bullets work fine in 20 round pmags, though they do not work in GI mags. I do not have M4 Feedramps.

Nature Boy · Jun 30, 2018

I don’t load for this cartridge so don’t know the specs. What about brass trim length? If it gets too long it can pinch the bullet and cause pressure issues.

Likely not the problem, just throwing something else out there to check

mjsdwash · Jun 30, 2018

neck diameter is .333-.335, so that may be something. BTW IwI is IMI

mjsdwash · Jun 30, 2018

fat necks will be where I start, but looking through what I have, only one was fat, and only .001 over. Still, Only a few had the primers go, so that may be it. 243Winxb chart, this is the only sign of pressure. Its a starting point, but if anyone has any more thoughts, I will listen. I forgot to mention, and its important, NONE of the 110Vmax loaded with 20grains of H110 had issues, and I reloaded those cases a few times, only the light loads have issues.

Walkalong · Jun 30, 2018

What is the neck thickness of the converted brass?

A chamber cast is easy to do, what is the diameter of the neck area of a loaded round with the converted LC brass.

243winxb · Jun 30, 2018

mjsdwash said:
Not sure what the OAL is at the moment, but the bullet is seated about halfway in the neck, and are not touching the rifling.

Seating bullets deeper, shorter OAL may reduce pressure? https://forum.nosler.com/viewtopic.php?f=4&t=28209

Case Capacity may make a difference in pressure? I dont do water. I compare weight. Note: Noslers water capacity is with bullets seated. Doesn't seem usefull.

Some converted 223/5.56 brass gets neck reamed when converted to 300aac.

Just some more areas to check if its not a thick neck issue.

mjsdwash · Jun 30, 2018

Walkalong said:
What is the neck thickness of the converted brass?

A chamber cast is easy to do, what is the diameter of the neck area of a loaded round with the converted LC brass.

nominally .010

Walkalong · Jun 30, 2018

mjsdwash said:
nominally .010

That should be OK, assuming they all are.

mjsdwash · Jun 30, 2018

Walkalong said:
That should be OK, assuming they all are.

looks like a few are not, but still cant see .001 making more pressure than 3 grains of powder. Its weird. I may have to buy some legit factory ammo and load those cases to failure to see if its just the brass.

Walkalong · Jun 30, 2018

No, .011 should be fine as well.

243winxb · Jun 30, 2018

Tumbling media left inside brass will raise pressure , its another possibility i seen online.

SCC · Jul 1, 2018

In the handloading section of 300blktalk IMI brass is listed in both the good and bad conversion lists with the following note:

Note 4:
This brass is included in both the good and the bad list based on differing user reports. It is important to keep in mind that sometimes a single headstamp can be made at multiple factories on multiple differing manufacturing processes. Other times a manufacturer that has their own brass factory might bring in brass from another manufacturer during times of high demand or to fulfill a large contract.

ETA: This is due to varying case thickness which results in varying neck thickness after conversion.

WestKentucky · Jul 1, 2018

First thing to look at is the primer pocket process. Are you swaging, or cutting the crimp out? If cutting you may be cutting out too much, and if swaging you may be pushing too much material out. I would be checking dimensions on my tools, and checking for any variation in pocket size after cutting and then backtrack once I found any irregularities or any out of spec bits. It is odd that it's only with some loads, and even more so that it's light loads, but start where the problem is at and verify this us are good before you go looking elsewhere for an answer that may be right there that's being overlooked. Calipers are quick and easy.

mjsdwash · Jul 11, 2018

WestKentucky said:
First thing to look at is the primer pocket process. Are you swaging, or cutting the crimp out? If cutting you may be cutting out too much, and if swaging you may be pushing too much material out. I would be checking dimensions on my tools, and checking for any variation in pocket size after cutting and then backtrack once I found any irregularities or any out of spec bits. It is odd that it's only with some loads, and even more so that it's light loads, but start where the problem is at and verify this us are good before you go looking elsewhere for an answer that may be right there that's being overlooked. Calipers are quick and easy.

I do cut out primer crimps with a razor using the case mounted in a drill (very effective) and use pin gauges to make sure all is right. Given the tens of thousands of cur primer crimps using 5.56 and never a loose pocket in the same process I didn't worry about that. My initial thoughts on the light load issue was H110's reputation for unpredictability at low pressure, though its supposed to give extremely low pressure with light loads. Im thinking its a brass problem at this point.

mjsdwash · Jul 11, 2018

I loaded and shot 60 rounds loaded with the 110 RMR 30carbine bullets and 15 grains of 2400 using a new lot of brass with zero issues. I also ran an H1 buffer because I know primer issues can be caused by early extraction -though they're not supposed to fit back. The rifle ran like a dream, shot accurately and no primer issues, so Im assuming some of the issues were from marginal brass I picked up at the range. I have also read from several sources the 300 AAC just likes to loose primers due to the high and very fast pressure curve of pistol powders. One thing I did notice on the popped cases, the neck diameter was .307, and a bullet would not go back in. thanks for all the suggestion, I will keep reading if anyone has more

243winxb · Jul 11, 2018

hdwhit · Jul 12, 2018

What is the source of the converted brass?

I typically buy crimped 223 cases since the presence of the primer pocket crimp ensures that I am dealing with once-fired brass. Nevertheless, I have encountered more than one case where, after removing the primer pocket crimp, the primer entered the case without resistance, thus indicating the primer pocket was already expanded.

If you are reloading brass that was too hot when it was initially fired then there should be no mystery that the primer pockets might be expanded before being loaded for the second firing.

light load, loosing primers

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