Primers Blowing Out on Lake City Reloads for 300 BLK

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May 6, 2017
I recently started reloading, starting with 300 BLK sub-sonic. To date I have had 100% success with sub-sonic. I am shooting through a 16” barrel with AAC Cyclone suppressor.

Today I loaded my first supersonic rounds; using Nosler 125 gr. Ballistic Tip bullets, 17.8 gr of H110, CCI #400 primers and 2.060” OACL. Nosler lists the max. powder charge as 18 gr, which was the most accurate load that they tested. Everything worked fine, with the exception of the Lake City cases. Nearly all the LC cases blew the primers, some of the bottoms bulged and some had cut marks on the very ends.

The Gorilla & PNW Arms cases all worked fine. In the photo below, the two PNW cases in the black tray were factory 147 gr loads. The two PNW cases in the black tray with gold primers tray were 220 gr. Subsonic reloads.




Based on the reloaded Gorilla & PNW cases and fired primers, I am assuming that my Nosler supersonic loads are fine; and I just need to avoid reloading the LC brass. I believe that the LC brass came from some Freedom Munitions reloads I bought, as well as one other source that uses once fired LC brass.

Any input is appreciated.


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Case neck walls too thick? What does a loaded round measure at the middle of the neck?

0.332" I forgot to mention that I am using the RCBS AR Series Small Base 2-Die Set with Taper Crimp. And I check each round with a Lyman case length headspace gauge.
.332 should be OK, unless the chambers neck area is tight.

The two on the left are seriously over pressure.

The Gorilla case where the case head is swaged into the ejector cut out is also high pressure. Just not nearly as bad as the blown primer cases.
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You might weigh the cases and see if there is a weight difference between commercial and your Lake City. Regardless, I would cut the load on all of them as it is apparent that pressures are way too high.
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Even the PNW looks very warm to my eye. Perhaps the LC brass has less capacity, maybe the pockets were worn already or the necks need turning. It could be they sized down easier than the others and have increased space between the head and bolt face. If the others fit closer they may mask signs of pressure.
Did you start out at seventeen and eight tenths? Eighteen was the max for their rifle. Five percent less is seventeen and one tenth. Your chamber may be tighter.
Nevertheless all can be assuaged with powder, I believe you have too much. It would be easier to use less powder, than segregate cases or find wider primers. Albiet, this is all just conjecture and opinion.

And finally, WELCOME!,welcome to the best, most knowledgeable site about a firearms and their care and feeding. One would be hard pressed to find a more helpful group of humans anywhere.
Shoot well. And take care so you may shoot often.
I appreciate all of the replies. The Hornady link and discussion about pressure and suppressors is very helpful. I was not thinking about the published loads and how a suppressor affects things. I will certainly lower the charge, probably to 16 gr and see how it works from there.
Using LC cases vs commercial 308's usually needs them to have maybe 2 grains less powder or pressure will be very high. That's likely what is going on with your Blackouts. Not to say you cannot use LC cases, just that they'll need their charges reduced when compared to the other brands.
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i load 17 grs H-110 with 130gr serria in LC cases in a rem model 7 aac with no problems. eastbank.


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I remember reading a post about the differences with and without the can, had to do with the Recoil/Buffer/Buffer Spring Tension and their performance. Don't remember the specifics, might be worth researching.

I am fortunate, my 10"SBR 300 AAC and 10" 5.56 both work flawlessly with and without the Can. I just don't see the purpose of Subsonic 5.56/.223. I have plenty of 22LR bullets.

Good Luck, the Blackout is a Knockdown, Drag Out Blast to Load and to shoot as well. I love mine..
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I found this article regarding pressure someone linked to at the facebook group “RELOADING 101: Learning the Art”:

This is an excellent article. All of my primers that did not blow out are cratered and I clearly have ejector ring printing on most of the Gorilla and PNW Arms cases. For the Lake City brass, it appears that the shoulder area expanding and deforming allowed the primers to more easily pop out.

The Gorilla brass are from their Troop line which they state are once fired, converted Lake City Military brass cases. Here are some average weights, sampling 8 - 10 of each:

Lake City – 83.7 gr
Gorilla Troop – 82.9 gr
PNW Arms – 84.5 gr
Hornady – 81.6 gr (from new 208 A-Max rounds)

Another thing I thought about is that I have no clue how many times the non-Gorilla LC brass has been reloaded. These were more than likely from the Freedom Munitions reloads. Perhaps some of these cases were already subjected to overpressure events. In hindsight, when hand priming, I recall some very easily installed primers. And my ignorance loading too high for a suppressed rifle pushed them well above their limit.

Hopefully I did not damage my rifle. I will thoroughly clean and inspect is today.

Again, I appreciate all the responses and input.
I will certainly lower the charge, probably to 16 gr and see how it works from there.
Loaded rounds neck diameter- When 223/5.56 brass is formed into 300 BLK, the neck wall thickness must be checked. If the loaded rounds neck diameter is larger then .334" the rounds bullet may get crimped in the chamber on loading.

The area where the neck meets the shoulder may form a donut, maybe even after a few loadings??

When the bullet can NOT exit the case fast enough on firing, very high pressure is the results. I think this is what happened to the LC brass.

I know Walkalong pointed this out in post #2, but its worth keeping an eye on , and double checking.

If a tight neck on some is the problem, reducing the powder charge to 16 gr may not help.

Primers- I would not use CCI 400 as they flow at midrange pressures for me. But yours seem to be holding up better than my lot. Your firing pin channel/hole must be smaller than my bolt action.
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I cleaned and inspected my rifle, especially the bolt assembly, the carrier group and chamber. Everything looked fine. So I took much slower today, inspecting each spent case before moving on to the next round.

I think it went much better today. All rounds are still using H110 with CCI #400 small rifle primers.

The two Hornady and two Gorilla rounds each had 15.6 gr. And the two PNW Arms had 16.0 gr. Two primers flattened more than others. In the future, I will try using the Winchester WSR primers, which I already have in hand.


I think keeping it between 15.6 gr and 15.8 gr would work the best for this Nosler 125 gr bullet in my suppressed rifle.

Thanks again for all the help. This truly is one of the most knowledgeable and helpful sites I have found to date.


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