Brand new rifle, sheared case

[lennyo3034]

A friend of mine tried to shoot his brand new custom rifle today. Fired 3 rounds with this result:

Load was:
41.0 gr H4350, Sierra 142 MK, CCI LR BR Primers, and Hornady Brass. 5X fires

Any ideas on cause? I was thinking headspace, but the top brass chambered into another gun without issue. Not as good as testing with a no go gage but it shows the brass didn’t expand way too long.

 

[918v]

Too much shoulder bump.

 

[McNamara0851]

Use a comparator and measure the top case and an unfired case from base to shoulder.

 

[Sheldon N]

Too much headspace.

If your buddy doesn't have a comparator, he could do a rough check by measuring OAL of a empty case that hasn't been fired yet, then adding layers of tape to the case head until he couldn't chamber it in the rifle, then measuring OAL again.

 

[lennyo3034]

He doesn't, but i'll be seeing him this weekend and will bring mine.

 

[Singleshot]

Yikes. Any damages to the rifle?

 

[Deleted member 10043]

Don't shoot that custom POS until it is fixed.

 

[lennyo3034]

No damage to the rifle that he can see.

I’ll bring some factory ammo for him to try as well. After we test headspace.

 

[Steel head]

Yikes!

 

[antithesis]

Too much shoulder bump.

I agree. Looks like the typical result from continually FLS with the dies set to make contact with the shell holder. Case head separation happens around the 5 reload when you do this and run near max. 41.0 of H4350 with a 142 SMK, and OAL of 2.800 is close to 58k psi. If you get a warm lot of powder you can hit 68k psi.

If the smith is reputable then headspace is likely not the issue. I always check, but most of those guys are crazy concerned about shipping something that is not in spec.

 

[supercorndogs]

I agree. Looks like the typical result from continually FLS with the dies set to make contact with the shell holder. Case head separation happens around the 5 reload when you do this and run near max. 41.0 of H4350 with a 142 SMK, and OAL of 2.800 is close to 58k psi. If you get a warm lot of powder you can hit 68k psi.

If the smith is reputable then headspace is likely not the issue. I always check, but most of those guys are crazy concerned about shipping something that is not in spec.

Powder charge has very little to do with CHS. It is stretching the case at the web as the shoulder moves forward. 41g of h4350 is generally not a hot load anyway.

 

[Singleshot]

Never had to happen, but good to know.

Does the bolt get stuck? Also, what can be done to prevent this? Neck size only, or minimize shoulder bump?

 

[afv338]

i had this happen to me years ago, sent a rifle to a smith he cut the chamber for a standard rem recoil lug and not the new one which was thicker. i stared shooting it with factory ammo. didnt inspect any empty's, and case head separation from excessive head space. almost lost my eye fucked up the gun. dont shoot that gun again it could cost him his life. it sure looks like to much head space to me.

 

[antithesis]

41.0 is or is not hot depending on case volume and seating depth. QuickLoad is your friend.

 

[supercorndogs]

41.0 is or is not hot depending on case volume and seating depth. QuickLoad is your friend.

Why don't you explain to us how you came up with 58k with none of that info, and how it changed to 68k from a "hot lot of powder." If you put in the wrong info, you get out the wrong info. Quick load is not your friend, its a tool, use it wrong and its pretty useless.

The old Hornady 140 match ammo load was 41.5 of H4350 with a 140 a max.

 

[antithesis]

Obviously you don't use the software, and yes it is a tool. So sure, this is how:
142 Sierra MK
Case length 1.910
OAL Seating depth 2.800
Case capacity 51.20 (my average fire case capacity)
41.0 H4350

Truncated results:
+00.0 101 41.00 2731 2351 57295 8284 98.9 1.303 ! Near Maximum !

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba 101 41.00 2838 2539 67418 8039 100.0 1.219 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba 101 41.00 2583 2104 47356 8152 94.1 1.413

 

[918v]

Powder lots do not vary by 20% (+\-10%), certainly not current lots of H. 3% is more like it. Get a real chronograph, not some optical pos.

 

[supercorndogs]

Obviously you don't use the software, and yes it is a tool. So sure, this is how:
142 Sierra MK
Case length 1.910
OAL Seating depth 2.800
Case capacity 51.20 (my average fire case capacity)
41.0 H4350

Truncated results:
+00.0 101 41.00 2731 2351 57295 8284 98.9 1.303 ! Near Maximum !

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba 101 41.00 2838 2539 67418 8039 100.0 1.219 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba 101 41.00 2583 2104 47356 8152 94.1 1.413

Plus minus 10% is 5% either way. You are showing a 20% plus minus. A 10% difference in lot to lot burn rate. I doubt it.

 

[antithesis]

Ignorance is bliss. Unwatch clicked.

 

[Rocketvapor]

Who needs common core math when you have software

 

[lennyo3034]

Builder is well known. I highly doubt they screwed up headspace that bad. Don’t want to drag them through the mud when it most likely isn’t their fault.

5x fired Hornady brass is likely the issue. He has shoulder bumped after every firing. I will bring tools this weekend as well as some factory ammo.

In the meantime, I’ve told him not to shoot it. Will update.

 

[Steel head]

I bit more history on that brass might be interesting.

 

[Xander3Zero]

Although it is unlikely that over-pressure caused that CHS... in the second picture the primers look very flat. It is blurry and not a great angle, but the edges of the primer cup look very sharp and crisp.

 

[supercorndogs]

Although it is unlikely that over-pressure caused that CHS... in the second picture the primers look very flat. It is blurry and not a great angle, but the edges of the primer cup look very sharp and crisp.

Flat primers can be a sign of excessive headspace. The firing pin pushes the case forward, then the case head gets a running start at the bolt face.

I had a lyman 223 die that would produce CHS in one firing when cases were sized all the way to the to the shell plate. A couple of them fully separated like #2 in the picture. All had very flat primers.

I had some 6.5 creed that did it at about 3 loadings due to a chamber that would close on a field gauge, and .007 shoulder bump. So I order some proper measuring tools rather than using the method of easing the die down until the case chambers. These started to show cracks but never actually separated. {because I trashed them of course}

A human hair is about .003.

 

[Rlandry]

You should know what your headspace is and be bumping the shoulder for .002" (if it's a bolt gun)
Go/No Go gauges definitely have a purpose, but keep in mind that the SAAMI spec covers a .010" span between min & max while the gauges are only .004" apart. If your chamber is cut long and you are oversizing and bumping too far, that would account for at least part of your problem. Also, the case with the big dent looks like it may have been sized using too much lube.

 

[Sheldon N]

Also, the case with the big dent looks like it may have been sized using too much lube.

The dent is from the escaping gas from the case head separation.

 

[bax]

Could be fairies or dragons or trolls or a 3-headed cow but I'm going with - sized the cases too much, pushed the shoulder down too far. I have a gallon ziploc bag half full of incipient head separations I have collected over the years including 50 Lapua 308 cases where I did exactly that and screwed up every one.

Pull trigger, firing pin pushes case forward against the shoulder, primer fires, building gas pressure holds the forward end of the case tight against the chamber walls, the base of the case is pushed back to the bolt face and the case splits at the web. The most dangerous part is the high-pressure gas flying around. In a Remington 700, a small bit of smoke will come around the bolt face. In picture 2, I see light strikes - that matches. I get it is pedestrian, even ordinary and common, but I submit, the most probably cause.

Yes,

• check the headspace. (I have gauges, mine are in spec. My process would catch this.)
• If the barrel was removed, make sure that it is tight - at least 30 ft-lbs of torque. (I have done this)
• If he has two guns in that caliber, make sure he didn't exchange the bolts. (I have not done this)
• If he has two shellholders that fit 6.5 Creed, maybe he used the wrong one.
  • My favorite trick is when the lock ring on my die gets loose and I don't notice. My process catches that, maybe his process doesn't.
  • (I have done the two shellholder thing so then fixed my process)
• If he borrowed that ammo from someone and he has any of that borrowed ammo left, he should give it back - that ammo doesn't work in that gun. (I saw someone blow up a gun doing this)

I don't shoot that caliber so I don't know if that load is hot but speaking about QuickLoad, I have been reloading since about 1970 and I have never seen two lots of the same powder that varied by 10%. As far as I know, I have never seen variation of more than about 2%. Sure, 10% is possible and maybe he is just pouring in a little RedDot to supercharge his load - but the simplest explanation is usually right, see above. Let's start there.

 

[McNamara0851]

I purchased a lot of 500 “once fired” Norma 6xc that were oversized by ~.020”. I’m assuming the previous owner ran his die down to the shell holder and sized them all. 3-5 firings in they started cracking at the case web.