The Base Guard bullet is made either in a LSWC-1 die (if you don't mind the shoulder of a semi-wadcutter design), or in a regular three-die set such as
the FJFB-3 (for smooth ogive bullets). Base Guards are remarkable in their simplicity: a disk of copper, which starts out with a conical shape with a
hole at the peak, is dropped into the die and a piece of lead is put on top
of it. The assembly is squeezed under tons of pressure, flattening the disk
and making it grow until it hits the die walls. Then it forms a
forward-pointing scraper edge (burnishing tool edge) toward the softer lead
and away from the hard punch. This edge, when driven down the bore, seals
gas and removes leading from the bore. It is not necessary to use lubricant
or hard lead with these bullets, even with velocities as high as 1,400 feet
per second, in most guns.
The BGK-1-R is slightly different from the dies for Corbin presses, because a reloading press generally does not have proper ram clearance at the top of the stroke for swage dies. In type -S and -H dies, the slot in the die is below the press head. The die is installed from the bottom, and is screwed upward into the press head (just the opposite of most dies that fit the press head). In the -R type, the slot is on top. The die is made extra large diameter to give it strength for cutting against the otherwise unsupported top end of the die. Using your -S or -H dies in this manner will cause them to snap off at the slot! Do not use the -S or -H type die with the slot on top of the press head. Doing so will void the warranty and probably break the die.
The lower portion of the die is a guide for the punch. It is only necessary to move the ram far enough to clear the slot so you can advance the copper strip, and then raise the ram just far enough to cleanly punch through the strip. This is a very short motion, usually less than half an inch. Therefore, you can adjust the die so that the copper strip is punched through at the top end of the stroke, just before the ram runs out of movement. This gives you much higher leverage and makes the operation easier than if you try to use the punch to push the cut disks all the way out the top of the die on every stroke.
The stack of cut disks in the top of the die will move out the top as you continue to cut more disks. If a disk tips sideways or jams, causing hard operation and excess effort, simply lower the die and push all the disks through to clear them, then adjust it back to the higher position again. A light film of Corbin Swage Lube wiped on both sides of the strip will help reduce friction and increase the life of the punch.
Materials other than Corbin's .030-thick copper strip may cause a problem with improper shape due to the resistance to being punched. The small post in the punch contacts the strip first, and pushes a cone shape into the strip before it punches through. Since different materials may resist stretching or punch through either more easily or with far more force, it is possible that they might not form the cone, or might fail to punch out the small hole in the center of the disk.
Using iron or steel sheeting, or hard brass, may cause damage to the punch or die. Although other materials may work, it is best to use Corbin's CU-5 or CU-50 copper strip, which is a deep drawing grade with good surface finish and deburred edges, with proper anneal and good tolerance control. It is 0.030-inches thick with a 1-inch width. Small disks can be cut from one edge, and the strip turned over so that another row can be punched from the other edge. Larger disks may be economically cut by allowing a staggered double row, with the disk centers offset from one side to the other.
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CORBIN, PO Box 2659, White City, OR 97503 USA