Neck Separation at shoulder – post firing, post neck turning operations

[RonR]

Neck Separation at shoulder – post firing, post neck turning operations

Had this happen last Thursday evening with my son at the range.

The neck came out from the chamber after I tried chambering another round without realizing. A brass filing about half neck diameter in length, similar to neck turning filings, was barely visible when viewing down the barrel at the range at what appeared to be near the start of the rifling. You can just make out the filing on the patch above where the neck is in the picture.

Fired 13 prior of the same recipe (4 @.030 off lands, 8 @ .020 off lands and 1 @.010 off lands) with no issue. Chambered perfectly and extracted with no extra effort at all. See picture below of loaded ammunition to determine the order at which it occurred…and the remainder of loads to be tested.

A few questions
1. Has this happened to anyone else?
2. What are the possibilities of root cause?
3. Will annealing the cases prevent this from occurring?


Some of my thoughts are
- Federal brass…reports I’ve read here not all too positive compared to other options
- The failed brass is not work hardened enough with firings - having too much of a ductile situation perhaps ( to clarify I don’t believe it’s a work hardened situation ) This was just a factory fired round that received OCD case prep.
- Neck turned too far into the shoulders
- I don’t believe the load is too hot
- rifle is ok to continue to use?

Below some note on process etc that should be reviewed. Please note that this is the first time using neck turned brass for us and that I am a sophomore reloader. The objective of neck turning brass is for process repeatability and the pleasant byproduct so far is the tightest results to date. Encouraged but this failure is concerning. No problem with brand new PRVI brass in my son’s savage with same process but slightly thicker neck.

Thanks for your time. Best regards
Ron

Picture of necks - shown is the "dirtier" side of the neck. The other 3/4 of circumference does not have this occurrence.

Picture of primers - appear normal to me

Case Prep
- Factory fired Federal brass – no other reloads on this failed case. ( 9 previous non failing cases were the same. 4 other successful cases were factory + 1 reload in this past range session)
- Primer pocket reamed
- Flash hole de-burred
- Shoulder bump
- Chamfer/trimmed
- Neck turned to .0115 neck thk into shoulder approx .030
- K & N neck turning system
- Note no failures on 20 rounds on brand new PRVI brass that got the same treatments except for .012 neck thickness on/for my son’s savage

7mm-08 recipe for bolt action Savage
- Win 760 43.5gr starting load from Lee data
- Sierra HPBT 140gr
- Federal case
- Federal 210 large rifle primer
Loading method
- Shoulder bump
- Neck size to produce .002 neck tension
- Prime
- Dry lubricant with motor mica (white stuff)
- Load powder
- Seat bullet with much more precision and repeatability than ever before

Picture of remaining loads to be fired indicating the order of firing and the separation occurrence

 

[Kryogen]

did you notice any gain in accuracy on neck turned vs non neck turned cases?

Turning weakens the cases, so the point where you stop the turning has to be weaker.

Could happen?

No clue sorry.

 

[bsand]

Isn't federal brass much much softer than prvi? Could be part of the reason the other ones didn't fail.

 

[Andy]

IMO it's not due to your load, but your brass prep. As you suggested was possible, it looks like your neck turning thinned the brass at the neck-shoulder juncture and when you neck-sized then inserted the brass you left it hanging by a thread. It was probably the extraction, not the firing that separated the neck from the shoulder. It would be interesting to see what the brass looks like sectioned.

 

[Hitzy]

Isn't federal brass much much softer than prvi? Could be part of the reason the other ones didn't fail.

It's soft, and usually quite thick compared to other brands. I've cut open lots of .223/308/30'06 and found that's a consistent trait. I suspect the softness and thickness go hand in hand.

 

[big boar]

You turned INTO the shoulder by .030". I know you should turn into the shoulder (to avoid "donuts") but not sure you need to turn into it by that much. Also you're down to .0115", what is your original unturned dia? I've not turned 7mm but for a 308 that starts at .015 I get by very well just by going to .014. Have you turned too thin AND too far down?

 

[RonR]

did you notice any gain in accuracy on neck turned vs non neck turned cases?

Turning weakens the cases, so the point where you stop the turning has to be weaker.

Could happen?

No clue sorry.

Increase in accuracy yes. For most, these results might be embarrassing but for me, it's pretty good considering a bullet and powder I've never used before. 1st try at any combination after neck turning. (Auditing the process. ) I'm in it to have repeatable reloading process first, and accuracy gain is a secondary anticipated result. The Federal brass was all over the place giving me different seating forces and different seating depths. The neck turning solved all of that. Apologies for the rotated image but it tells the story.

Regards
Ron

 

[RonR]

Isn't federal brass much much softer than prvi? Could be part of the reason the other ones didn't fail.

That's what I am thinking. Hopefully others can comment. I do know that turning the PRVI brass was more consistent than all the Federal stuff I have.

Regards
Ron

 

[RonR]

It was probably the extraction, not the firing that separated the neck from the shoulder..

Interesting thought Andy. The edges look stretched. It would line up with soft ductile brass thinking then...at least I think so. Harder brass wouldn't pull apart then???

It would be interesting to see what the brass looks like sectioned.

I have got a machinist neighbor. Perhaps I can get him to section some existing brass to see if there is this donut phenomenon.

In terms of depth into the shoulder, from what I've read, 1/32 is used. http://www.accurateshooter.com/technical-articles/reloading/complete-precision-case-prep/.

Thanks for the response Andy. It's something else to consider.

Ron

 

[RonR]

It's soft, and usually quite thick compared to other brands. I've cut open lots of .223/308/30'06 and found that's a consistent trait. I suspect the softness and thickness go hand in hand.

Yes...I am starting to lean that way. I'll fire some factory +1 and factory +2 to see if it recreates itself.

Andy mentioned the pulling apart the neck from the shoulder when retracting the bolt and I am beginning to believe that concept. I feel a little better now.

Much obliged Hitzy.

Regards
Ron

 

[RonR]

You turned INTO the shoulder by .030". I know you should turn into the shoulder (to avoid "donuts") but not sure you need to turn into it by that much. Also you're down to .0115", what is your original unturned dia? I've not turned 7mm but for a 308 that starts at .015 I get by very well just by going to .014. Have you turned too thin AND too far down?

Hi Big Boar,

The accurate shooter article is the source for that value of .030. .012 neck thickness was the mark but better measuring equipment and measuring loaded rounds with math confirmed that neck thickness was a little under. .012 was some information found on Mystic's site I believe. I too was concerned that there is a point at which cutter angle and shoulder angle would meet but I think what Hitzy has stated that the thickness and the ductility being high in this case worked hand in hand to be the source of the failure.

The federal brass thickness was all over the place and varied all the way down the neck. I would have stopped at .014 or .013 but there was so much surface that wasn't turned that I stopped at .012. My next brass purchase will be Lapua to get away from the inconsistencies so that I have more range time and less prep time.

Thanks for weighing in Big Boar!
Regards
Ron