Gunsmithing Question: 300 Win Mag Cases dimpling at the shoulder?

[reewik]

Ok so I have read, and read, and read... did I say I have read about this. I am sorry but this will be long so I can provide as much information as possible.

Info
Brass that has experiences this phenomenon:

Hornady 3rd load
FMMG 2nd Load
Gunwerks 2nd load

Dies: Whidden full length and micro seating dies.

Powder: H1000 @ 78.6g
Bullet: 208 ELDM
OAL: 3.51"
Primer : CCI Magnum Primers

Rifle is a GA Precision built 300WM with a 24" barrel using an AEM5 30 cal can.




Ok so I loaded up some brass to fire form the brass to my chamber. After the first shots with the new brass all the brass averaged a head space size (using the provided Whidden gauge) of 2.269. I resized the brass pushing the shoulder back .002, (or so I thought, the push back was actually .007) the first time this problem occurred so I corrected the die to only push the shoulder back by .002) during the full length resizing process for the FMMG and the Hornady brass.
The very next shots exhibited a shoulder deformation (referred to as dimpling in the reading I have done) and some signs of head case separation and cracked cases at the head. So I trashed all the brass and ordered up some of the Gunwerks brass.

In the time I waiting for delivery I did run a bore scope in the barrel and looked for any sort of damage or carbon rings. There were no signs of any issues the barrel looks good. I then did a thorough cleaning of the bore and the barrel anyway just to start with a clean setup. I remeasured the head space two different way. I used the Hornady tool and measured the head space several times. I then disassembled the bolt including the plunger and used an unused NEW Hornady case I still had and seated a bullet long. I seated and re-seated until there was no bolt hang up and measured that. I ran a go and no go gauge and all checked out just fine.

One I received the brass and loaded 50 rounds to fire form 50 cases. I loaded 10 of each of the following charge weight 72.5, 73, 74, 75, 75.5 grains of H1000 with the 208 ELDM's, same primers all at an OAL of 3.51". I took those fired cases and measure the head space once again on several cases. I adjusted my resizing die out making sure not to push the shoulders back at all so I just resized the body and the neck. I checked the case OAL and all was within spec. This time I loaded 75.5 G H1000 as this is what yielded the most consistent ES of all the fire form loads.

I fired 10 rounds and while I did not have any case separation I did experience the dimples on two of the 10 case shoulders after firing. So I read and researched some more and decided maybe I was not getting enough pressure so I re-seated the rest of the same loads to an OAL of 3.43.

I went back to the range and shot 10 rounds of the 1 time shot Gunwerks brass with 75.5g of H1000 with an OAL of 3.43" @ 2910fps on average with no shoulder issues. Just for grins I had some of the same rounds in the bag loaded to and OAL of 3.51" and the first shot dimpled the shoulder again so I shot no more that day.

I am lost. I have been reloading for over 20 years and never have I experienced case head separation or this dimpling of the brass like my 300WM does. Any advise?

 

[ShtrRdy]

I'm a little confused. In the second paragraph you mention measuring headspace, but it sounds like you're determining where the bullet touches the lands. Please clarify.

Would you please post a picture of the "dimple" effect. I'm not sure I know what that is.

From what I understand from your description I'm surprised that you are getting case head separation. When I first started reloading for the 300 Win Mag I was pushing the shoulder back too far when resizing the brass. On the third loading some of the cases started to crack in the area of where a case head separation would occur. Once I started to limit how far back I was pushing the shoulder I haven't had a problem.

 

[reewik]

Your right, I confused my terms.. I did both measurements. My mind was working faster then my fingers I guess.. Here is a pic of the "dimple". The case brass that had total case separation had 4 of those.

 

[ShtrRdy]

Oh, wow, that is a serious dent. I can't come up with what might cause that upon firing and extraction/ejection. Hopefully someone will know.

 

[AIAW]

Usually you see that then the shoulder doesn't expand quick enough (via low pressure) to create a seal, which causes the gas to leak around and dimple the case. That's roughly the same charge I use on the 208's though.

Are you annealing? Sounds like work-hardened brass to me perhaps.

 

[Vargmat]

I have had that happen to me as well. Both times it was with Norma brass that had 6 or 7 reloads with no annealing between. I think that AIAWs diagnosis is correct on this. The brass has become too hard to seal the chamber. This is my first magnum caliber rifle so I cant compare but I would guess that setting of +74 grains of powder each firing is pretty tough on brass and I dont expect it to last as well as the brass for my 6.5x47 Lapua does.

 

[reewik]

AIAW,

I am not annealing the brass. Keep in mind there are only a max of three firings on my brass and the brass is experiencing this issue. The new Gunwerks brass should not need to be annealed so soon as it was the second firing of the brass. I am having to jump the bullet quite a bit because of the chamber length. I do not expect to be able to get as many reloads as the non magnum calibers but two firings is not gonna be good.

Vargmat,

I agree that after 6-7 loads the brass will harden but like I said these are 1x to 3x shot brass.

My guess is I either need to re-barrel and start over. Maybe I just have a worn out chamber. I am lost as to how to solve the issue. But I am not going to give up!

 

[Pinmaster]

Just chiming in... since reewick is a buddy of mine.

The gunwerks brass is annealed out of the box so shouldn't it go 3-4 firings before needing to be annealed again?

His rifle did pass the go and no-go headspace gauges and the chamber looked carbon fee with my borescope.

To watch his 300wm chew up brass is puzzling.

 

[AIAW]

AIAW,

I am not annealing the brass. Keep in mind there are only a max of three firings on my brass and the brass is experiencing this issue. The new Gunwerks brass should not need to be annealed so soon as it was the second firing of the brass. I am having to jump the bullet quite a bit because of the chamber length. I do not expect to be able to get as many reloads as the non magnum calibers but two firings is not gonna be good.

Vargmat,

I agree that after 6-7 loads the brass will harden but like I said these are 1x to 3x shot brass.

My guess is I either need to re-barrel and start over. Maybe I just have a worn out chamber. I am lost as to how to solve the issue. But I am not going to give up!

I agree, it shouldn't but you know how that goes sometimes!

The only other thing I can think of is that they are headspacing off of the belt instead of the shoulder. First firing typically the belt is setting the headspace. All subsequent firings you typically want the shoulder to determine the headspace.

If it's indeed the belt setting the headspace this might explain what is happening to cause the lack of sealing. What I would do is fire them but do no sizing afterwards (other than neck only for tension). See if that makes any difference. I think your shoulder bump may very well be taking the headspace away from the shoulder, and giving it back to the belt. Just a guess there.

 

[ShtrRdy]

Read entry #4 of this thread for a possible explanation.

Dimple in Brass Cases

Had two strange occurrences while shooting some reloads at a range last week. I fired 10 reloads each of a 7.62x54R load using Varget, IMR 4895 and BL-C(2) and ten reloads of a .303 British using BL-C(2). The last fired case for the 7.62x54R using 41.0 gr. BL-C(2) (starting load as listed...

www.milsurps.com

Here's another discussion

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[Pinmaster]

That is a good read ShtrRdy .

My 300wm with the 208Eld-M's have an OAL of 3.62 (2.884@ Ogive) whereas his are shorter. I know that the chamber on my stock rem 700 barrel is long, but other folks load data that I have seen posted here and on other websites are all close to 3.6x with the 208's. Heck my chamber is so long that I could go longer if the rounds would fit in the AI mag.

Reading post #4, does it seem that his seating depth may be related to the issue?

 

[reewik]

Lots of good info so far.. keep it coming. I will remeasure everything again!

 

[ugsly308]

Have seen similar cases in two 7 RUMs. Called Hodgdon and they said the case fill/charge wasnt enough to seal the case. They told me to either up the charge or switch powders to get a better case fill. Not sure if that the case here but I'll just throw it out there.

Casey

 

[reewik]

I can up the powder charge... but I am already getting good speeds and I really feel that moving above 2950 may sacrifice accuracy. By seating the bullets in further I should have increased the pressure however I am super jumping now. I am really trying to keep the velocity down and H1000 is such a good powder for the 300. By the way as far as case fill, I hear a small crunch when seating to 3.43" OAL. so there is not a case capacity issue. Matter of fact the gunwerks brass is thicker so I have less capacity then I did in the Hornady brass.

 

[AIAW]

You have any H4831SC in your stock? Might could try it out also just to see. It's an excellent powder for that bullet weight.

 

[reewik]

I can always go get some however I am not sure I will get the speeds I am looking for. Just a thought but what if I increase neck tension by .001 instead of seating the bullet in further? Right now I am using a .333 bushing and have a .332. Does anyone think I could fix the issue this way?

 

[AIAW]

I can always go get some however I am not sure I will get the speeds I am looking for. Just a thought but what if I increase neck tension by .001 instead of seating the bullet in further? Right now I am using a .333 bushing and have a .332. Does anyone think I could fix the issue this way?

I wouldn't go deeper if you are already compressing the charge. Neck tension - maybe? Hard to say, but worth a try. Theoretically neck tension would increase start pressure slightly.

Like I posted earlier also - try no shoulder bump on some cases and see how that does at the same charge and OAL. Are you needing that bump to chamber them or was it just sort of part of your process and may not be needed? The goal is to not headspace off of the belt.

I'd like to see if @spife7980 has seen this before also.

 

[reewik]

I am already no longer bumping the shoulder on the most recent loads. I can still chamber the brass without the bump. I am also looking to keep the OAL at 3.51" like your saying. I did not make that clear on my last post. What I am going to do tonight is to remeasure everything. I am then going to reload the 10 cases I just shot with a different .332 bushing to increase the neck tension by .001. It is hard to understand not sizing off the belt but I get it. The belt hits a "wall" in the chamber. I have always struggled with this rifle for reloading maybe I am just a dufus...LOL I am also going to load up some 190's because I know they do not mind jumping and now that I think of it if I am going to load more 208's I have to get some because I only have 2 left.

I really appreciate everyone's input in helping me figure this out.

 

[Cheyenne Bodie]

I think that the differential pressure between the exterior of the shoulder and the interior is acting in an asymmetrical fashion. Sounds obvious, but what I mean is that the exterior pressure doesn't need to be especially comparatively immense itself, it just has to trend existing physical stress toward a failure location where it then further takes the path of least resistance.

I'd try a different powder, doubt you're far under spec for the 208 H1000 load max already. If you're measuring belted carts accurately and everything else is good to go, that's all I can really think of. I avoid crunching powder whenever possible, but I've never really heard of a legitimate account of it leading to a problem. Maybe annealing is the problem like was also already mentioned, but I kinda doubt it. I'm assuming you've inspected the rifle chamber and it checked out.

 

[supercorndogs]

Have you tried it with out the can?

 

[reewik]

Nope.. not on these loads