View Full Version : What would cause these cases to split??

November 5, 2006, 11:14 PM
I went to the range over the weekend to run some rounds through my Ruger Mark-II M77 rifle in 7mm Remington Magnum. I've been reloading rounds for that gun for several years without any problems.

While at the range, I pulled 4 rounds out of my case and fired them. After I was finished, I looked at the brass and noticed that 2 of the rounds had split around the base of the case. These are the same loads I've always ran, but I though that maybe I just had few week cases….or I had reloaded that batch one to many times. After looking closer at the rounds, I noticed that the other two rounds that did not split had rings around the base....it looks like they were just about ready to split.

Well, after I saw those cases......I decided to switch over to some brand new in the box Federal store bought rounds. I fired two of those through the gun and noticed that they had the same rings around the base…it looks like they were ready to split out also. What would cause this???

After I got home I went through all of my brass from rounds that I had previously fired through the rifle, and none of them had those rings around the base of the cases….even cases that had been reloaded 6+ times.

What is causing this??

Here are some pics.




November 6, 2006, 01:51 AM
Well I'd want to headspace it first..

I'd also look at the extractor to make sure that it is not "holding" the round by the rim when it's breeched for some reason..Could have a lot of debris at the collar connection not allowing the extractor all the way forward. However, I'd think there would be feeding issues with this...

November 6, 2006, 02:02 AM
Can we get a picture of the base of the cartridges?

November 6, 2006, 02:59 AM
Are these splits only happening on Federal brass?

November 6, 2006, 06:13 AM
What you see is a classic headspace problem. The fact that you've loaded the first cases many times without problems, then get separation with both handloads and factory ammo indicates a rifle headspace problem. If it had only occurred with handloads, I'd tell you to back off your sizing die to get the cases to headspace on the shoulder.

You need to get the headspace on your rifle checked before you get some case failures and it spits hot brass at you.

If the headspace is excessive, the action could have been sprung by hot handloads and may have been weakened. It may be best to send it back to the factory. They can test the metal and replace the receiver, if necessary.


Mike Irwin
November 6, 2006, 10:22 AM
Agree with Picher. You've got either a big problem with your rifle, or a big problem with your reloading processes.

You need to figure out which one before you have a really nasty problem.

November 6, 2006, 10:29 AM
Thanks for the info guys.

I'll get some pictures up of the bases of the cases later tonight. I will take the rifle in and have it checked out. I'm going to be really surprised if I have "sprung" the action......all of my handloads are under max load....and I've been using the same load since I've had the rifle and never had any problems.

November 6, 2006, 10:37 AM
Here is a picture of the bases. The first two on the left are the reloads that actually split out. The two on the right are the brand new federals out of the box that also got the rings around the base. Same shells in the original pics above.

November 6, 2006, 10:51 AM
When they started to use belted cases they sometimes got careless with shoulder dimensions . That has caused problems. First I would check the headspace. When reloading always size to that particular chamber, not to any average, or new case .That will take care of any sloppy chamber cutting they might have done.

November 6, 2006, 11:22 AM
Just to eliminate your handloading practices as the problem, why not go buy a box of loaded factory ammo and see what that does? If you get the same rings, something is wrong with the rifle.


November 6, 2006, 11:44 AM
Just to eliminate your handloading practices as the problem, why not go buy a box of loaded factory ammo and see what that does? If you get the same rings, something is wrong with the rifle.

I am pretty sure he already tried that with the same results...
Well, after I saw those cases......I decided to switch over to some brand new in the box Federal store bought rounds. I fired two of those through the gun and noticed that they had the same rings around the base…it looks like they were ready to split out also. What would cause this???

Art Eatman
November 6, 2006, 11:49 AM
Another vote for some sort of headspace problem. But, since the case headspaces on the belt, it seems to me that the bolt is not going as far forward as it should.

I'm gonna move this thread to the gunsmithing forum.


November 6, 2006, 12:04 PM
I am pretty sure he already tried that with the same results...

Oops, sorry. I read that as "bought some new _cases._"

Well, if the rifle does it with brand new loaded ammuntion, I don't see how it can be anything OTHER than a rifle problem!


November 6, 2006, 01:16 PM
*** Well I think I may have figured it out!! ***

After looking at the 4 pieces of brass I fired after I had the two reloads split on me....I noticed a pattern. They all of the same "ring mark" around the base. I mean the exact same markings!

In other words....I think when those two hand-loads split on me....it marked the chamber some how, either with powder residue or something else. Then every case I fired after that point (including the Federals out of the box) got the same ring around the base becase when the shells expanded, they were marked by the junk left in the chamber after those first two split on me.

Look at the picture......those are the two Federal cases.....they both have the same marks on them. After looking at the rest of the rounds, they all have the same marks also.


November 6, 2006, 02:17 PM
Might still be a good idea to have a good smith look at the gun and check with some go, no- go gauges. Better safe than sorry.

James K
November 6, 2006, 02:37 PM
Well, those Federal rounds are not "just out of the box", they have been fired. What you have is excess headspace, period. If you want, you can try another ammo brand, but I think you will have the same result.

I don't know what loads you are using, or how much you have fired the rifle, but with a rifle with its original bolt and no tampering, excess headspace has only one cause - worn or battered locking lugs or lug seats.

Barring some wrong "gunsmithing", you have simply worn out that rifle, and I suspect your reloads have been pretty hot, which is a big factor. I would return the rifle to Ruger; whether they can fix it, I don't know, but I wouldn't trust anyone else to try.


Jim Watson
November 6, 2006, 02:39 PM
Bear in mind that the chamber headspace specification for a belted cartridge is the width of the rim + belt, nominal .220". Shoulder location can get a bit sloppy in those guns and lead to case stretching no matter what the gauge says.

November 6, 2006, 03:11 PM
I bought the rifle brand new about 4 years ago. I've always used loads under "max load", and I've never had any kind of problems out of the 300+ rounds I've ran through it.

I'll have the headspacing checked just to makesure....but if it is a headspacing problem, it just doesn't make sense.

If I had a headspacing problem, why have I fired some brass 6 or 7 times, and have never had that ring around the case? Now everything I fire thought the gun has it? Just doesn't make sense to me.

November 6, 2006, 05:54 PM
If you push the shoulder back when sizing the cases, the belt controls the headspace. That causes cases to stretch too much and reduces case life to only a few reloadings.

I back the dies out a bit the first couple of times I reload some cases for a rifle, so only about 3/4 of the case neck is sized, then I check to see if the case chambers easily. If it does, I'll load all the cases that way until it's difficult to chamber rounds.

For the next reloading, I turn the die in a little at a time, until the case chambers easily, then set the lock ring as the perfect fit for the rifle. That way, the shoulder of the case should be supported and case stretch is minimized. This is no secret. It's in most loading manuals and in some die adjustment instructions over the years. Ammo loaded this way is also more accurate because the case fits the chamber almost perfectly.

Magnum pressures cause cases to not last as long as those shot with more moderate pressure. If case separation is imminent, or occurs with cases that have been reloaded too many times, don't shoot any more of them. Pull the bullets and save the powder. You could be saving an eye or more! Sixty thousand pounds of pressure acts like a cutting torch if there's a way for it to get out. You don't really want to be in the way of that blowout!

Reloading manuals are there to be read...c a r e f u l l y!


November 6, 2006, 07:09 PM
What you need to do is get a 1 inch micrometer and understand what correct readings are supposed to be just above the belted cases on a NORMAL CASE. Learn to use the 1 inch micrometer, good ones should be able to read to within 10 thousands of an inch. Don't quote me because I don't reload, You should be able to get by on only measuring to within 1 thousands of an inch. I don't know too much about case stretching but I do know that the case will stretch "there" where you are suppose to measure and I suspect You cannot resize that area of the case. If some proves me wrong it's OK because I don't want to spread misinformation. That area that burst is one of the warning signs that went past the warning . I believe that you are supposed to mike cases at this particular point each and every time that you reload, especially a 7mm magnum.

James K
November 6, 2006, 09:13 PM
With a rimmed or belted case, if the headspace is good, an oversize chamber or an undersize round will not stretch as those have. The case will simply fire form to match the chamber.

I will say again, the only reason for that kind of case separation is excess headspace. The fact that it shows incipient separation with new cases pretty well rules out overworking the brass as the primary cause (though it can make the situation worse).

I agree that the amount of firing done and the use of normal loads should not result in a headspace problem so soon. That is one reason I recommend sending it back to Ruger; if it looks like a manufacturing defect, they may well repair or replace it free of charge.

But I think you can be sure of one thing - it is only going to get worse, and perhaps very quickly.


November 6, 2006, 09:24 PM
It's hard for me to believe that you have built up excessive head space in a gun like yours just yet. Let's rule a few things out first. Take one of your recently fired brass, decap it and put a good dial caliper on it and see if it has stretched beyond allowable limits for your gun.
When you seat the bullet and load the rifle dont let the bullet touch the lands, it builds too much pressure, if it is a moot point ignore it.
I find it hard to believe that headspace is lost from a Ruger M77 from 300 rounds, I am not ruling out headspace. Get a set of go and no-go gauges or go to a gunsmith and get it checked out like you said but I would like to lay odds that you are developing too much chamber pressure for either the weak brass that you have,improper resizing or seating of the bullet.

November 6, 2006, 09:58 PM
imq707s: I agree that the new brass seems to reflect debris in the chamber caused by the case separations and not necessarily thinning of the case due to excess headspace. The only way to be sure is to cut a case in half longitudinally and check for thinning in the area ahead of the web.

It's a good idea to mike the case head, but it won't tell you anything if you mike the area ahead of the belt, because even if there's thinning at that point, pressure pushes the exterior out to meet the chamber walls.

The places to measure are at the head at marked locations and/or at the belt, since those areas aren't restricted by the chamber. A good test is whether the primers seat too easily or not. If they do, the head has expanded from high pressure.

Misfires aren't common on belted cases because if the case is too short, the belt will stop it from sliding ahead in the chamber. On non-belted cases misfires and pierced primers are common.

You may not have mentioned trimming cases, but I hope you're keeping them within allowable limits. Cases that are too long can increase pressures.

I had a Savage 110 back in 1961 that had a loose chamber, though still in tolerance. We loaded ammo on my buddy's press set for his Mod. 70 Win and it had a tight chamber. I experienced numberous misfires, primers popping out, pierced primers; all the signs of excessive headspace or overloaded ammo. The rifle was returned to Savage and they checked it and found it to be within tolerance, but replaced the bolt. I still had problems until I got my own reloading press and set the dies according to instructions.


November 7, 2006, 06:46 AM
Picher That's a good point to remember on allowable limits on the length of the case.

Hunter Customs
November 7, 2006, 08:33 AM
I would have your gunsmith check the headspace and while the gun is in the shop I would have him make a cast of the chamber using cerrosafe.
The reason I suggest the chamber cast is I believe you may have some gas cutting from the splt cases; the cerrosafe cast will show this if it's so.
Bob Hunter

November 7, 2006, 10:28 AM
Well I looked down into the chamber of the rifle and I can definitly see some markings in the chamber. I'm going to try to use a brass brush (12ga) and some copper solvent to clean it out and see what that does.