I was out shooting my old Ruger 300 WM this afternoon getting ready for a trip across the pond this summer.

While out shooting this afternoon, I noticed a piece of brass that had pretty severe signs of a case head separation about to occur. So, upon futher inspection of some of the fired brass there was quite a few more in the pile. I'm on my third firing of this brass, and the brass not yet fired a third time show absolutely no external signs of case head separation. To say I was surprised to see this would be an understatement. I'll check for internal signs with a paper clip once I break the remaining cases down.

I've only neck sized this brass, so I'm leaning towards a headspace issue with the rifle. This gives me another reason to put a new tube on it. I've never been happy with its accuracy.

Here is a crappy picture I took with my cell phone showing the case head separation starting.

If you have only neck sized, I would agree with you on a headspace issue........ 300 Brass should last quite a few more reloads using sensible methods.

Factory rifle? Or already a re-barrel?


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It is a factory barrel. I know that it has an excessive throat because I run out of magazine capacity long before I even attempt to get close to the lands.

I'll use it on this trip and it can visit the gunsmith once I return.

yup - new barrel

I would suspect the brass before the rifle. Ruger does use long throats but I have not had one with headspace out of spec. But anything is possible. Remember, belted brass and chambers, are measured to the belt only; shoulder position is not a factor in the headspace measurement. Neck or full length sizing has no impact on the headspace in belted brass. For best results, I make them headspace on the shoulder.
Do other makes of brass do the same thing?

Brass from this particular lot is W-W Super.

I've got another set of W-W Super brass that will be on it's 4th firing the next time to the range. I annealed the brass after the 3rd firing and will see what it does next time out.

dpcd, you mention headspacing off the shoulder, if I'm only neck sizing the brass, am I NOT headspacing off the shoulder with no shoulder bump back as in P-FL or FL sizing? Obviously there is some room in the chamber to allow the brass to move forward (stretch). This allowance shouldn't be from the neck sizing because the shoulder is not being moved. Correct?

quote:

Originally posted by graybird:
Brass from this particular lot is W-W Super.

I've got another set of W-W Super brass that will be on it's 4th firing the next time to the range. I annealed the brass after the 3rd firing and will see what it does next time out.

dpcd, you mention headspacing off the shoulder, if I'm only neck sizing the brass, am I NOT headspacing off the shoulder with no shoulder bump back as in P-FL or FL sizing? Obviously there is some room in the chamber to allow the brass to move forward (stretch). This allowance shouldn't be from the neck sizing because the shoulder is not being moved. Correct?

Are you absolutely sure you have your die set up correctly??? It would appear that you are somehow pushing the shoulder back during sizing. I don't know if that is even possible with a NS die??
Either that or you have lug set back.
Try some factory loads or try setting your die up so it only sizes to within .050 or so of the base of the neck.

If it truly is headspace and knowing you have a low shot count on that rifle I'd just set the barrel back one turn and re chamber to bare minimum go

umm the round headspaces on the belt...
so there ain't no way it's a headspace problem.

quote:

Originally posted by Lamar:
umm the round headspaces on the belt...
so there ain't no way it's a headspace problem.

Funny

Right; what I usually try to do with belted cases, (which in no way to the book headspace numbers use the shoulder for that dimension); I treat them like rimless cases and make the bolt close with a "feel" on them. I have found that the tolerances allowed for the belts is generous, leading to the problem you have. Sometimes it means treating them like a wildcat and moving the shoulder forward. If you are neck sizing, you aren't touching the shoulder, which means they are still relying on the belt to headspace. In this case, there is excessive headspace, likely caused by the brass and nothing you are currently doing will change that.

quote:

Originally posted by dpcd:
Right; what I usually try to do with belted cases, (which in no way to the book headspace numbers use the shoulder for that dimension); I treat them like rimless cases and make the bolt close with a "feel" on them. I have found that the tolerances allowed for the belts is generous, leading to the problem you have. Sometimes it means treating them like a wildcat and moving the shoulder forward. If you are neck sizing, you aren't touching the shoulder, which means they are still relying on the belt to headspace. In this case, there is excessive headspace, likely caused by the brass and nothing you are currently doing will change that.

But after you fire them once or twice.......yu are no longer headspacing on the belt if you only neck size.

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This is a common problem on ALL belted magnum cases. If the chamber is just a slightly large in diameter in front of the belt, the cases expands to the chamber walls. A slight bulge is formed. While you may not see it, you may feel it as you can your bolt shut.
A normal sizing die being used to "neck size" will still push the ring back in a little. This flexing of the brass causes it to fain just in front of the belt.Now,add this to a slightly long chamber and you have very short case life.
This problem is so prevalent that there is a fellow making special dies in all belted magnum calibers that stops this problem from happening.
I've been told by others who shoot a lot of belted magnum rifles that as many as 6 out of 10 rifles will have the chambers cut "a little too large" causing such short case life.
http://www.larrywillis.com/
The guys who use his dies say that they are getting much longer case life. The die is not cheap,but my magnum brass is two bucks a case or more. It is worth the extra to save the brass cases.
I had my chamber cut to a very tight tolerance and this problem is not a factor in my rifle.
So far I have gotten four reloads out of each case with no signs of a stretch. I'll keep my figures crossed.

Tex; it is too late then; the stretching damage has been done. And since brass can withstand far more pressure than we think (see Ackley's tests), unless the case head is firmly against the bolt face the first firing, the brass will continue to stretch.
Separation caused by oversized chamber? If that were the situation, it would happen with all rounds fired and reloaded from large chambers and that is not the case. I think the promotion of good case care and tight shoulder to base dimensions is the cure and not working the brass in that area is a benefit. Moving brass in and out is not what causes the stretching; moving part of it rearwards whilst the front part is obturating, does.

I set my calipers to 0.220" to test the length from brass base to the top of the belt. When comparing the set caliper to the brass, there was a noticeable difference with the brass being shorter.

I measured about a half dozen pieces and they ranged from 0.211" to 0.213", so I guess I'd have an additional 0.009" to 0.007" of headspace along with the factory differences on the initial firing.

Just for giggles, I tested the inside of some 3x fired brass with a paperclip from a different lot of brass, and could feel a slight indention suggesting this set of brass is about to fail, too. Neither sets of brass has any inclination of case head separation from the outside with visual inspection with the exception of those already observed.

This suggests to me that with the base to belt being short and the excessive shoulder headspace this set of brass failed quicker than the other set I have that has the correct base to belt measurements.

I think I'll still have the barrel set back and chamber recut to see if that helps the situation, but it may not happen until after my hunt in June.

I wish you had a new brass datum measurement vs once or twice fired to show just how much strech you are getting

Get a neck size die and some new brass. Problem solved.

Might take a look into the 'Belted Magnum Collet Sizing Die".

http://www.larrywillis.com/

Neck or collet sizing won't help on a belted case that is fired in a long belted chamber. The problem won't be solved; it will continue as long as the brass is shorter than the chamber. Head to Belt dimension. Here are the numbers; brass min is .212. Chamber max is .227. So, we can have .015 (fifteen thousandths) of excess headspace. If you had a rimless case with that much excess headspace you all would scream and holler that it would kill you. (it won't) The only way to fix the situation is to set the barrel back for minimum brass, or treat the brass like a wildcat and fire form them; and use the shoulder as a headspace datum point.

+1

quote:

Originally posted by dpcd:
Tex; it is too late then; the stretching damage has been done. And since brass can withstand far more pressure than we think (see Ackley's tests), unless the case head is firmly against the bolt face the first firing, the brass will continue to stretch.
Separation caused by oversized chamber? If that were the situation, it would happen with all rounds fired and reloaded from large chambers and that is not the case. I think the promotion of good case care and tight shoulder to base dimensions is the cure and not working the brass in that area is a benefit. Moving brass in and out is not what causes the stretching; moving part of it rearwards whilst the front part is obturating, does.

Ok. I get it......that's why you think it's a brass problem. Thanks for taking the time to explain that so I could get it through my thick skull!

I shoot a 7mmRM a bunch and have reloaded the same lot of brass for it 10 and 12 times. I use PFLsizing and the "willis" collet. But if my brass was too hard, or shoulder back too far, on the 1st firing I would get the damage, and case head seperations in many less reloads. I use win brass and shoot it till the necks split.

Yes, if you have excessive headspace, you will get brass separations. We just notice it more on belted cartridges because it seems there is more manufacturing tolerance allowed. Now, if you oiled your brass first, that would not happen. Do not do that though. Might be that the factories are afraid to make belted brass to max dimensions as it is harder to squash solid metal into a chamber than it is for a rimless case. Just my supposition on that.
Best case is for the extractor to hold the case firmly against the bolt face but don't count on that, to counteract firing pin fall, which pushes the case forward.

quote:

Originally posted by ted thorn:

quote:

Originally posted by Lamar:
umm the round headspaces on the belt...
so there ain't no way it's a headspace problem.

Funny

I couldn't resist...
anyway the true cause has been pointed out.

once the work is done to the rifle you should see an increase in case life and most likely an increase in accuracy too.

Actually, it is a headspace problem. Headspace on belted ammo is from the bolt face to the front of the belt. Shoulder has nothing to do with it, but you know that.

quote:

Originally posted by Lamar:

quote:

Originally posted by ted thorn:

quote:

Originally posted by Lamar:
umm the round headspaces on the belt...
so there ain't no way it's a headspace problem.

Funny

I couldn't resist...
anyway the true cause has been pointed out.

once the work is done to the rifle you should see an increase in case life and most likely an increase in accuracy too.

In the event you didn't get it, ole Ted there was being facetious.

Hey!

Every time I try to be funny here I get put on someone's ignore list so I have to be careful. I accept full responsibility for everything, whatever it was. My wife blames me for it, whatever happened, or whatever I said.

I received some once fired military brass this afternoon.

I took a few measurements to see what the potential extra headspace might be on my rifle.

Here is a piece of brass shot out of my rifle:


A piece of brass from a sniper rifle (assuming the snipers are still using 300 WM)


And, another piece of brass from a different rifle. The firing pin marks were either smaller, or larger, I don't recall, but definitely from a different rifle.


What do you guys think about the extra 0.01" + headspace on this rifle, assuming the sniper rifles chambers are correctly cut?

quote:

Originally posted by ted thorn:
I wish you had a new brass datum measurement vs once or twice fired to show just how much strech you are getting

That is in no way a Headspace measurement; it is a case shoulder to head dimension, which is not the SAAMI method for measuring headspace on belted cartridges. If the military rifles (Remingon s) are "correctly" cut, with a SAAMI spec reamer, that dimension can vary up to .016 from a max chamber to a min spec brass. And so can the belt to head variance. I listed the tolerances above. And it is not controlled as well as head to belt distance. And that is not controlled well at all; that is why, historically, that belted cartridges are known for short case life. Best way to solve it is to actually treat it like a rimless case, as has been explained above.

quote:

Originally posted by dpcd:
That is in no way a Headspace measurement; it is a case shoulder to head dimension, which is not the SAAMI method for measuring headspace on belted cartridges. If the military rifles (Remingon s) are "correctly" cut, with a SAAMI spec reamer, that dimension can vary up to .016 from a max chamber to a min spec brass. And so can the belt to head variance. I listed the tolerances above. And it is not controlled as well as head to belt distance. And that is not controlled well at all; that is why, historically, that belted cartridges are known for short case life. Best way to solve it is to actually treat it like a rimless case, as has been explained above.

Damn it graybird

Everything has been laid out as remedial as posible

I hope you get this cleared up before we head over to Africa in a couple months

to make this clear in your head.
you have now compared to 2 other rifles and they are much shorter.
if you wanna see the rings appear again.
make sure those two pieces of brass chamber in your rifle.
load and fire them both just neck sizing them.
now look for the case stretch again.
you'll see it.

your chamber is too long for normal 300 WM brass
either make it from a longer case to fit YOUR chamber, or get the rifle fixed.
never mind the belt it's in front of the belt where the issue needs addressed.

You got it, Lamar. That was the reason for posting the second set of pictures comparing the brass from two different rifles.

I tried neck sizing (using a neck sizing die) the once fired brass yesterday, but there was too much swell at the base to chamber in my rifle. So, I removed the expander ball and sized the brass with the bottom of the die flush with shellholder.

The interesting thing about this exercise was how much the brass actually grew. The brass grew from 0.002" to 0.004" in the brass I checked. I assume this growth is attributed to the brass in the case body needing to go somewhere, so it went up making the case base to shoulder longer.

To make it perfectly clear, I could care less that the case headspaces off the belt, as I'm only concerned in the shoulder to base measurement; thereby, headspacing off the shoulder.

All this damn talk about belts.

You gals will be talking about matching purses and shoes soon

You could just handle it like a wildcat then, and fireform NEW brass to your chamber by seating bullets in NEW brass out into the lands and fireforming.

I would think this would solve your problem without rechambering.

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