Case pressure

[Herd Thinner]

So I am definitely a rookie of reloading so with that: today I was shooting my AR-10. The reloads in question are mixed once fired cases. I have lee dies. I full length sized the cases. Reloaded 100 rounds. COL 2.010 to 2.015. CCI 200. 41G Imr 4064. 165 g sierra. Fired 3 rounds and the fourth case split in half. Part dropped from the mag well the other was actually pulled from the throat. My question is was it a weak case or maybe I mis trimmed and it was 2.016-2.020. I spot check with the Wilson. Do I need to use SB dies when on an AR platform. What am I missing. The gun was clean and has 273 rounds now 277. The charge was correct. The correct primers. My crimes where not overbearing. What other info would help. Thanks in advance.

 

[Rangemaster]

Where you crimping the brass? I should the same loads and never had one split the brass. I never crimp also, just seat.

 

[Herd Thinner]

I do crimp. The crimps were not excessive IMO.

 

[jet_lagged]

"....the fourth case split in half. Part dropped from the mag well...."

So I think we are talking about case head separation, not split necks? If you do not know the history of the brass and it was once fired in a M-60 or something with a fairly loose chamber, then full length resized, you may have more problems.

See paperclip test to check the cases......

The Rifleman's Journal: Reloading: Case Head Separations

 

[Herd Thinner]

"....the fourth case split in half. Part dropped from the mag well...."

So I think we are talking about case head separation, not split necks? If you do not know the history of the brass and it was once fired in a M-60 or something with a fairly loose chamber, then full length resized, you may have more problems.

See paperclip test to check the cases......

The Rifleman's Journal: Reloading: Case Head Separations

I was just reading that article prior to viewing this...small world.....

I misspoke the spilt meaning the the case cut in half aka head separation ...........I cant seem to upload a picture but the picture in the article should just be my case ......
As for the history....I know it came from a machine gun....M60 maybe not sure ....I did full length size before using it ....

Thanks for the Intell.....

 

[mtHunter82]

I did this once in a FAL rifle. If your mixed brass is military, you MUST reduce your starting load by 10% and work up. The brass is thicker, so there's more pressure.


Sent from my iPhone using Tapatalk

 

[My Toy]

I just started dealing with once fired brass to feed my AR-10. My observation is that in any particular lot of once fired brass the cases may have been fired in a lot of different chambers (some much looser than others). I had a similar experience with my first batch of once fired brass. I had two near head separations out of 100 rounds fired on my first load; since then I've loaded that brass two more times with no problems.

Another poster on this forum talked about a method to sort once fired brass (before you size it) to segregate out cases depending on their once fired expansion; I modified his method slightly. Granted it is hardly fool proof but at least it is pretty quick and gives you some idea where your "new" once fired brass stands. I also was able to get brass of all the same head stamp so that eliminates one variable.

The method uses a cartridge headspace gauge (mine is a Wilson). I first de-cap and tumble the brass to get it reasonably clean. Next drop the un-processed case in to the cartridge headspace gauge and note how far in or how far out it protrudes. I divide the amount of protrusion in to 5 categories and drop the tested case in a different bin numbered 1 through 5. First category is: the case completely drops in to the gauge and can be dumped out without force; Second: case goes in all except for rim and needs to be pushed out; Third: case protrudes with rim and groove showing; Forth: case protrudes no more than 1/8" past groove; Fifth: case protrudes more than 1/8" past the groove.

I used the bent wire test on samples of cases and for the above categories 1, 2, and 3 I really can't detect any thinning of the cases indicating eminent separation. The bent wire test on samples from category 4 were iffy. The bent wire test on samples from category 5 (and I tested all of these) invariably detected a definite groove of thinning just above the case web (although none of these cases showed the bright ring around the outside of the case above the head).

Again, I got this idea from another member on this forum (his name escapes me for now as far as giving him credit-- I could probably locate it if your interested). Seems like a great idea for quickly giving you an idea about the potential longevity of your "new" once fired brass.

As a side note so far out of about 1500 case run through this method about 10% fell in to category 5, 10% in to category 4, and the balance 80% in categories 1 thru 3.

 

[punkwood2k]

Quick question regarding case thinning.... When is the best time to inspect for thinning at the case head? Before or after tumbling / resizing? I know some do it at the beginning of the prep process, and some do it after all the prep work, because a clean case is easier to see it or something. I inspect every case after every firing, but I havent been reloading rifle cartridges long enough yet to actually come across an incipient separation yet (at most, 5 firings of a lot so far), so I'm still not "experienced" in spotting the signs...

 

[My Toy]

Quick question regarding case thinning.... When is the best time to inspect for thinning at the case head? Before or after tumbling / resizing? I know some do it at the beginning of the prep process, and some do it after all the prep work, because a clean case is easier to see it or something. I inspect every case after every firing, but I havent been reloading rifle cartridges long enough yet to actually come across an incipient separation yet (at most, 5 firings of a lot so far), so I'm still not "experienced" in spotting the signs...

In my opinion it would be after tumbling and before sizing. I believe signs of incipient separation are more visually noticeable and can be more easily detected on the case interior at this point.

 

[KYpatriot]

Some great advice in the thread already, I would add make sure you are not sizing the cases too much, only bump the should maybe .003 if you are sizing too much the case must stretch at firing at can pull apart.

 

[Herd Thinner]

In my opinion it would be after tumbling and before sizing. I believe signs of incipient separation are more visually noticeable and can be more easily detected on the case interior at this point.

Thumbs up on this.

 

[Herd Thinner]

My conclusion on my issue was this: for some reason in my rookie head I trimmed to 2.015 thinking it was better and some of the rounds may have been over the max trim. Add on a slightly harsh crimp and a weaker case. BOOM. Head separation. So I will tear down all my reloads. Resize using SB dies and trim to 2.005. Once again the information base on this forum is a life saver. There is no book that has all the reloading know how. Its good to learn from others.