The Norma cases that I have been using for the load development are starting to stretch beyond the maximum length point on the Wilson case gauge. Also the number of firing, and reloading cycles are approaching the point that the brass, especially the neck, and shoulder area, are becoming work hardened and will start to crack.
The answer is to anneal the case at the neck, and shoulder area. This is a process of heating the brass to a temperature that softens the metal making it malleable. The main difficulty with this process is heating the neck, and shoulder with out also over heating the lower body of the case near the web of the case where the head rounds ”up” to form the body. Each time the case is used for a firing, and loading cycle the brass will stretch a certen amount in this area no matter what, and if excessive heat is allowed to move into this part of the case during the annealing process the brass can become weak, and a case head separation can occur, ether partial, or full.
In the most extreme cases this could lead to the destruction of the rifle, and injury to the shooter. The one time I had a round suffer a full case head separation was with a M1a (M14) rifle resulting in the following round jamming into the remaining portion of the broken case still stuck in the chamber. This was with surplus military ammo produced in the late 1960’s that I bought, and used in the late 1990’s.
In 2015 I had bought 50 Lake City 7.62×51 .308 Winchester surplus cases that were pull downs, (unfired ammo that has been disassembled, and sold as components), that I used for my Model 700. The case in the photograph was the first one of this batch to crack at the case head, by the fourth loading I had fourteen cases crack, so the cases were retired. This was not a big deal as the cost of .308 Winchester is relatively inexpensive, and many times once fired brass can be found on the ground at many ranges.
Whereas .300 RUM brass is hard to find ether as a loaded cartridge, or as a component, this makes it necessary to take care of the cases a very high priority. With this in mind I prepared to anneal, full length resize, and trim the cases to a uniform length.
First the annealing of the case with a Bernzomatic propane torch by rotating the case with my thumb, and forefinger in the center of the flame until the neck, and shoulder became slightly red. If the lower part of the case would started to become warm I would stop the process. Usually by the time the case started to warm the neck was the right color, and I would drop it in the small bowl of water to quickly cool the brass.
There has been billions, and billions of words written about the need to water cool the brass after annealing both pro, and con. I use the water to cool the brass mostly to keep from burning myself.
Once the cases are annealing, cooled, and then dried, they are then lubed and sized with the full length sizing die instead of the neck sizing die. Finally the cases are trimmed to a uniform length of 2.863 inches.
A short post about this will be put up separately.
Three loads were produced using 168, 175, and 225 grain match bullets. The 168, and 225 are produced by Hornady, and the 175 is produced by Nosler.
The 225 grain bullet is the the heaviest match bullet I can find at this time. I had to be a little creative in my load development by using the the Nosler 220 grain match load data. This can be a little tricky, compared to simply using the load data for one brand of a certain type of bullet with a different brand. Example a Hornady 168 grain match bullet load can with a little due diligence be used with a Sierra 168 grain bullet if you start at the bottom of the data, and work your way up.
The 5 grain difference on heavy bullets like these should not be much of an issue as long as I start at the bottom of the loading charts and work up with small increments looking for overpressure signs.
With this in mind I started with 73.0 grains of IMR 4320, and Federal 215 match primers for the 225 grain Hornady match bullet. The groups were ok, but once again they were not consistent.
The 175 grain Nosler load was made with 83.0 grains of RL22. The first time I have used this powder. The five rounds group was also unimpressive.
The 168 grain match bullet failed to impress also.
During the bullet seating process setting up the bullet seating die with the 225 grain Hornady bullet a sad loss occurred with the first try resulting in the crushing of the neck, and shoulder of one of the Norma cases . This was not because of the longer bullet but was caused when I was calibrating the setting on the die .
I wanted to be able to have the ram of the press in the fully raised position, then run the die down until it bottoms out on the ram. Then I would set the die at this length using the locking ring.
With this zero set all of the bullet adjustment would be a simple process of setting the bullet seating stem to the predetermined mark on the stem.
When starting the process of determining the setting depth for this longer bullet I ran the charged case with a bullet into the die seating the bullet, and wound up buckling the shoulder of the case. A little adjustment using a Canadian Loonie as a gauge on the top of the shell holder created the right amount of space between the top of the shell holder, and the bottom of the die. This will allow me to have a zero setting, and then the ability to adjust the setting stem to the correct setting on the adjustment stem.
This will make keeping consistent, and quick adjustments of the die easy with all the different weight bullets I am working with.
With all this work being done the goals of precise, and accurate ammo should be as easy as 123.