Case Head Separation

[AnthonyR]

 

 

This is some of my Dakota 20Tac brass that has been fired 6 times out of a lot of just about 100 cases

 

The case on the left came apart on me when I was sizing it and the rest in the pic all exhibit a line in exactly the same place.

 

A quick Google soon turned up what the cause was - Case Head Separation and I have used a bent paper clip to examine the insides of other cases in the batch, only in the case on the right of the pic can I feel any line on the inside.

 

My question should I just bin all the cases showing the line and keep using the rest or should scrap the whole lot

 

[1967spud]

defintly scrap those with the line and probably a belt and braces measure would be to get some more but keep the old

[Brillo]

I had the same problem with a 7.62 Sterling Enfield. I blamed the rifle which had a long military chamber but, in the end, it turned out that a wasn't full-length sizing correctly. I wasn't pushing the case fully into the die and this created a weak zone on the case which eventually caused a fracture.

I reset the ram to ensure the case travelled all the way into the die and the problem disappeared.

[Andrew]

If from the same LOT, pitch them all.~Andrew

[auquhollie]

I had the same a few years back with a 243 AI. I binned them all as mine went bang when i fired and its not a nice feeling when you get a face full of shrapnel. It turned out that when i was full length sizing them i was pushing the shoulder back to far and had excessive head space. When i set my die up correctly and bought new brass i never had the problem again and infact them cases lasted over 10 firings.

 

Just make sure that when you size you are only sizing back 2-3 thow. Otherwise you are work hardening the brass at the same point every time hence the line around the case and the separation.

 

Cheers

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[Ronin]

Scrap all, start again with new.

[AnthonyR]

Thanks for the help so far.

 

The cases are all from the same lot, I have examined all of them and by the time I had finished culling the ones showing a line I only had less than 40 cases left, I don't want to bin them but I really don't want any agro in the future so I think I probably will just to be sure.

 

So do you think I am doing something wrong, I bump the shoulders back about 2 thou after each firing using a Redding body die and then use a Redding bushing die to size the neck. If I don't bump the shoulders back the brass will not chamber after about 2 firings.

 

The load I am using is 23.2 gr of RL10X with a 39gr Sierra BK which is a pretty warm load but not too hot in my opinion, this rifle is seriously accurate and wouldn't want to change anything unless I have too but having said that unless I can find some more 39gr Sierra's soon I am going to have to change something.

[Andrew]

Thanks for the help so far.

 

The cases are all from the same lot, I have examined all of them and by the time I had finished culling the ones showing a line I only had less than 40 cases left, I don't want to bin them but I really don't want any agro in the future so I think I probably will just to be sure.

 

So do you think I am doing something wrong, I bump the shoulders back about 2 thou after each firing using a Redding body die and then use a Redding bushing die to size the neck. If I don't bump the shoulders back the brass will not chamber after about 2 firings.

 

The load I am using is 23.2 gr of RL10X with a 39gr Sierra BK which is a pretty warm load but not too hot in my opinion, this rifle is seriously accurate and wouldn't want to change anything unless I have too but having said that unless I can find some more 39gr Sierra's soon I am going to have to change something.

 

Well. Maybe it's warmer than you think??~Andrew

[kent]

Its either a bad lot of brass or too hot a load for that rifle. we all know some guns will handle a stouter load than the next, yet some choose to ignore the sign until its so obvious if its their gun that cannot take top end loads. For me personally it would be new brass and a milder load as a double bubble change at one go

[auquhollie]

Thanks for the help so far.

 

The cases are all from the same lot, I have examined all of them and by the time I had finished culling the ones showing a line I only had less than 40 cases left, I don't want to bin them but I really don't want any agro in the future so I think I probably will just to be sure.

 

So do you think I am doing something wrong, I bump the shoulders back about 2 thou after each firing using a Redding body die and then use a Redding bushing die to size the neck. If I don't bump the shoulders back the brass will not chamber after about 2 firings.

 

The load I am using is 23.2 gr of RL10X with a 39gr Sierra BK which is a pretty warm load but not too hot in my opinion, this rifle is seriously accurate and wouldn't want to change anything unless I have too but having said that unless I can find some more 39gr Sierra's soon I am going to have to change something.

 

 

 

 

 

Its not so much something that you are doing wrong but from what i found the nature of a body bump die. Go grab one of the old cases and run it up into your bump die. You will see that the line around your cases is very close to the bottom of the bump die. With a bump die you are not sizing the whole case, you are only pushing back the shoulder then your neck die sizes the neck (funny enough).

 

 

I was doing exactly the same mate, i swapped all my dies for a full length die and have never seen the problem again in maybe 8 calibers and thousands of reloads.

 

All this line is, is the weak spot that is unsupported when you use a bump die.....nothing more.

 

IMHO a full length die is far better anyway. For accuracy you need consistency, what better way to size brass consistent than with a full length die. Necking your brass and then bumping the shoulder every 2 firings isn't that consistent.

 

Hope this helps.

 

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[Swamp Donkey]

I can't find the thread, but will look later, but its about making brass last longer. When you size 'new' brass 'too short' creating excessive headspace, it stretches upon first firing, which creates a weak spot, ie, your shiney line. From there, it's downhill

I tried this out, had two pieces of new brass, took them with the hand press up the farm, tightly sized one, loaded the pair, and kept loading, trimming etc until there was any visible difference or noticeable size difference with a vernier. The sized piece had to be trimmed after the second loading, the non sized case took four shots before the lee trimmer made a cut. Quite how long either was going to last is an unknown as I ran out of time after 11 loadings. But, the case I sized from new, before it was fired, was looking decidedly worse for wear compared to the virgin one.

Hth

Pete

[Swamp Donkey]

http://www.loaddata.com/articles/PDF/Load%20Development%20May%2011.pdf

[DaveT]

JUST MY TEN-PENCE WORTH BUT........Are you all SURE that its a simple case of hot load and/or case being too short as a result of over-sizing?

 

At half way up the brass the break seems way too high for the classic case-head seperation?...unless the chamber is also radically long and the bumping is extremely over-done.

 

I use a body die and neck sizer combination in many calibres and have never seen any such problems.

[baldie]

There is nothing untoward there Anthony apart from the brass is simply worn out from shooting and sizing.

 

If the cases are only firing twice before requiring the shoulders bumping back, then the chamber is tightly headspaced, probarbly at 0.001" or even 0.0005". Nothing wrong with that at all, its where the accuracy is.

 

The cases are wearing a little prematurely possibly, because the body die is pushing the shoulders back too far. It could be pushing them back as much as 0.004" ie maximum headspace. This means they will stretch 3-4 thou over a couple of firings, hence becoming tight again.

 

This is overworking the brass causing your problem. Get yourself a Hornady headspace gauge and set the body die up to push them back 0.0005" if you are doing it everytime you load them. This wont overwork the brass.

 

Common problem in AR15 loads. Due to the maximum headspace used to allow a straight pull to function, then full length sizing the brass ever loading, some brands only stand four firings before they start to case head separate.

 

Dakota was made by lapua , there is a fair chance its similar to the very thin walled 223 match brass.

 

Bin it all. If you reuse the remaining 40, they will go on you on the next firing.

 

A chamber cannot be cut "over length" If it does not fall within the 0.004" between go and no-go , it doesn,t pass proof.

[AnthonyR]

Thanks for the replies some very good info there.

 

All my brass was sized before first use

 

I already have a Sinclair headspace gauge and on my gauge on brand new Dakota Brass measures 1.3585" and my fired & sized brass is coming out at 1.3520, I don't have any un-sized but fired brass at the moment but will get some soon, don't want to waste any bullets with the SBK's being in such short supply.

 

Looks like Dave (and others) might well be right and I working the brass a bit too much.

[kent]

I shifted to Comp shell holders and fitting the sizing via bolt feel a while back, very happy with the results. Never got on with neck sizing and shoulder bump dies personally. Still others will feel differently