"inspect your rifle brass "

[tj3006]

I read that in the speer manual back when i started reloading some 36 years ago !
  Maybe i should read that part again.  Had a near disaster with my 300 H&H.
     Case head separated leaving most of the case stuck in the chamber. 1st shot, of the day,
So i brought the rifle home, pulled the bullets, checked the charge weight, all was good. I know i used the Right powder, (the load in question is a 180 grain partition over 69 grains of RL-22), So i looked at the remaining cases and found a very slight ring just above the belt. can,t  feel it with my finger nail , but i can see it. 
   I got the stuck case out with epoxy, And i plan to show the cases and rifle to a smith and see if we can determine the cause,. 
Could be the chamber needs attention, I think i might see if my size die is set right to the point of that ring. And maybe a neck size die is a good idea ! Any input would be appreciated !
                      ...tj

 

[Encore64]

Not unusual with belted rounds. I usually start with new brass only. I seat the bullet to slightly engage the rifling and fireform with a reduced load. But, use caution!!! Bullets touching the rifling definitely increases pressure.

After that partial resizing and being careful not to set shoulder back. This allows headspacing off the shoulder instead of the belt.

[tj3006]

I started thinking about head space , right after i posted this thread, Fortunately i still have 20 fresh Hornady cases on hand, and i will fire form them with some round nose bullets i have on hand and will probably never use for hunting, Lets hope i can reach the lands with them.
...tj3006

[Encore64]

The other option is to neck brass up, then back down until brass seats with a slight resistance.

[AxeHandle]

Incipient Case-Head Separation in the thing to call it... Remember reading years ago that the M14/MIA high power rifle shooters kept count of firings and discarded cases after just a few firings.
bulletin.accurateshooter.com/2018/10/incipient-case-head-separation-how-to-detect-the-problem/

[zeus]

Did you bump the belt. That would do it for sure and can cause misfires.

[nicholst55]

The key to sizing belted magnum brass is to headspace the case on the shoulder, rather than the belt. Granted, that won't really work with the .300 H&H. Many magnum rifles have chambers cut that are very generous in length between the belt and case shoulder. This causes the case to stretch (grow in length) each time it's fired and stretched, sized (and shoulder set back excessively), and fired/stretched again. All of that stretching leads to head separation. If you adjust your sizing die to only bump the shoulder back around .003", this will minimize case stretching and the resultant head separation.

[bigbrowndog]

I bought a magnetic dial caliper for an engine rebuild years ago to measure flywheel run out, it makes a very handy tool for setting up dies. to just bump a case shoulder no more than, .003 inches.
There are tools made for the job but I had this available, and it works for ALL shouldered cases no matter the length, due to its own adjustment. I simply made an attachment to slip over the case mouth and touch the shoulder. This allows me to adjust dies to each chamber of rifle,......I also have dies for each rifle if the measurement for each chamber is greater than .006.

Belted mags are notorious for case head separation due to sizing to the belt instead of the shoulder.

Trapr

[bushog]

Fire once to form, neck size, fire at critter, into brass recycle.