[ngashooter]

I only own one rifle that uses a belted case, a 30-338 (which, other than neck diameter is the same case as your .264), single shot Mauser action gun built for 1,000 yard prone shooting decades ago so only have a little practical experience with them. From much that I have read, the belt was originally intended to prevent cartridges like the .300 H&H from having ignition issues because they did not have much of a shoulder to position the primer consistently against the bolt face. Belts then came to represent a symbol of a 'high power' cartridge so they were put on any round that the manufacturers wanted to 'hype', whether it really helped anything or not. The .264 has plenty of shoulder and doesn't 'need' a belt but, it got one anyway. If your .264 Mag seems to function fine with factory ammo you may not really have a rifle headspace issue but your sizing die could be short enough that you end up bumping the shoulder back and creating an ammo headspace issue. After checking your brass to insure that there isn't a really thin section right ahead of the belt (no point in tempting fate with more head separations) try turning your sizing die out a turn. Then work in slowly from there until the cases fit and you can close the bolt on the case with just a little effort.That will keep the shoulder where it fits your rifle and should prevent the problem.
That at least worked in my Wimbledon gun, I lost a number of cases to neck splits because I didn't know much about annealing 30 years ago but never had any head separations.

Bruce

Excellent advice! Thank you.

 

[jayhdavis]

I got out to test some more loads through the .264 Win Mag this morning. The first three test loads had fed, fired , and ejected fine but accuracy was less than stellar. I had hoped I could get to book max as listed by Hornady. They published 66.1 gr of Ramshot Magnum as maximum with their 140gr SST bullet. I had loads of 65.8gr and 66.1gr with me today. The 65.8gr load shot into 2 inches without any issues. I shot other guns while the barrel cooled. The first shot with the 66.1gr load resulted in difficult bolt lift. Yanking it up and back ejected a case with obvious problems. The case had partial head separation with a crack about half way around the circumference in front of the belt. I did not attempt to fire any more of those. I will pull the bullets and recycle the components. I will stay with the 65.8gr charge as it has good power View attachment 186527
and acceptable accuracy for my needs.
View attachment 186528 View attachment 186529

One of the problems with belted cases that are supposed to headspace on the belt is sometimes they don't. The only belted cartridges I have experience with were the 300 Win mag and the 350 Rem mag. It was highly suggested to me by people who know that when reloading those cartridges, I should neck size only. That way the cartridge head spaces on the shoulder ensuring longer case life and reducing the chance of case separation. That is what I did when I had those rifles and I had no problems.

 

[Robert70]

Hornady makes a good universal tool. I've used it extensively on everything I load. Measure a couple of fired cases and then set back shoulder .001 - .002 when sizing. It prolongs the life of the brass, reducing the need to trim. Adds to safety and enhances accuracy.

View attachment 186547

I recently bought a dedicated caliber RCBS Precision Micrometer gauge for my 30-06 1903A3. It is superior to the Hornady but limited to only one specific caliber. I don't know if one is made for the .264. If not the Hornady will suffice.

Bepe

Good call. I use the same Hornady tools.

 

[Bob Lewis]

I had that exact same problem with a Ruger 7X57mm and Winchester brass this was after about the same number of firings,3-4. After telephone conversations with Winchester, Ruger, Sierra and Hodgdon it was decided to try neck sizing only, this solved the problem. I have been getting more loads than I can count, also I trim to chamber minus 0.001"-0.002" for going book values.
I stared this process back before all this internet help and follow it with all of my bottle necked cartridges including the belted ones.

 

[Sr40ken]

I use the same tool Bepe recommends. Very sound advice. A valuable tool for bottleneck cartridges.

 

[Mowgli T.]

Full length sizing die could be the problem. Shoulder would be pushed back creating the same outcome as excessive head space.
Back in the day we were getting ready to resell some estate firearms. One magnum rifle was from the P.O, Ackley shop. Using the button headspace gauge it looked like excessive head space. Then we figured rightly or wrongly the seat for the belt was made deep so measurements would be from the shoulder. I think the caliber was 338 WinMag. This event was many years ago.

 

[Robert70]

Most all of the above info is helpful. Headspace could be an issue in any rifle. New, used or even a milsurp that's been rechambered to a 'sporting' cartridge. It's always a good idea to check it. Headspace 'go-no go' tools aren't that expensive. Even the AR platform uppers should be checked. Buying an upper that doesn't come with the BCG, should be checked also. Yes, there are those who say it needn't be checked. It's just 'Best Practice' to be sure.

 

[Mowgli T.]

I still have my old built up Mauser in 257 Roberts. That was built up with minimum had space and 1:12 twist for shooting 75 and 87 gr. bullets. I had a case appear to break like OP's magnum. I had written this off as brass had work hardened from over use. I had neck sized the brass. When case became hard to chamber it was time to full length size. I admit that was semi-voodoo reloading.This failure did happen right above where the web started. Those Roberts loads were top which may have aggravated the case failure.

 

[mrerick]

A quick look at your photos shows that your primer is backing out on the case that separated.

Get a set of headspace gauges. They are reasonably priced and worth it.

 

[Mowgli T.]

OP: That looks like the custom rifle you have featured here before. For me, a built up rifle gets tested for head space before first being shot. I'd suspect that there is nothing wrong with the rifle.The suggestion here is to neck size your once fired brass. On the other hand we don't know how the gunsmith breeched up the rifle. Remove all doubt and have the rifle inspected. You probably know an individual who is trustworthy to check the head space.