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Reloading Ammo: Cartridge Shoulder Bump − How Much Do You Really Need?
Cartridge shoulder bump is sometimes overlooked in the reloading process. But if special care is taken when resizing that element of the brass you can be rewarded with much more accurate ammunition and longer shell life.
Cartridge shoulder bump, eh? Nah, I’m not talking about some hipster dance, I’m talking about how much we move the cartridge shoulder during the resizing process.
Most folks (myself included) will resize a bottleneck rifle case so that it adheres to the specified SAAMI specifications, but that requires working the brass considerably. As we’ve all seen, overworking the brass will make it brittle, and cut the life of our brass much shorter than necessary.
In a lever action, autoloader or pump action rifle, the SAAMI specification is a necessity, but us bolt action nuts (again, I include myself in this group) can get away with a larger dimension, so long as it chambers properly in our rifles. What we’re after here is a smooth chambering case, minimally reduced from the post-firing dimensions.
The resizing dies are designed to give SAAMI dimensions, but by varying the shellholder, we can adjust, incrementally, exactly how much the shoulder is moved. For example, Redding offers a set of Competition Shellholders that vary by .002”, from .010” down to .002” of depth. They come five to a set, and are precisely machined, as are all of the Redding products. You can simply move the cartridge shoulder at .002” increments, until you find the dimension that fits easily into your rifles chamber.
Now, it may seem silly that a change in dimension of that minute measurement will make a difference, but it does.
There is an awful lot of stress on the shoulder of a bottleneck cartridge, during both the firing and resizing processes, and that constant working of your brass is what is reducing your case life. Keep that shoulder to a dimension that will move very little, and you’ll also experience increased accuracy, without the difficulty associated with neck sized ammunition.
You know, neck sized stuff is great to shoot, but closing the bolt can be a chore, especially when the ammunition is used for hunting. But, if we have minimally resized ammunition, so that the bolt closes easily, it can fill many needs.
In addition to increased case life, the ammunition produced with the Competition shellholders give the better accuracy I’ve mentioned by giving better cartridge concentricity. You see, the more precisely the bullet is aligned with the bore, the less the bullet has to move to align itself in the throat of the chamber.
These shellholders are also a fantastic tool for curing the problems associated with mildly excessive headspacing. Once you’ve fireformed the brass to the problem chamber, these little gems will help you do your best to keep them at that dimension, yet feed easy.
The Redding shellholders have a nice black oxide finish, come in a quality plastic case and are clearly marked with the dimension that they change the specification. Give ‘em a try; you might keep your brass around quite a bit longer.
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