The pressures used in bullet swaging can reach as high as that inside a high powered rifle chamber when the gun is fired. Because of the extreme pressure on the dies and punches, they are built of special high strength materials with extensive, careful heat treatment to insure that they will not only hold the pressure, but do it without changing critical dimensions over a lifetime of use.
The diameter of the dies and punches are fixed by their geometry, of course, but the length of a shouldered punch, or of a hollow point or cavity-forming probe on the end of a punch, can now be adjustable for greater versatility, with the optional type -HA, -SA, or -MA punches. The adjustment is made in one of two ways, depending on the particular purpose and design of the punch. Hollow point and other cavity-forming punches, with a projecting probe, are typically adjusted by removing a locking set-screw in the head of the punch, and turning the slotted or hex-cavity adjustable rod which is part of the probe, to make it project a different amount from the main body of the punch. The locking set screw is then replaced to hold this new setting securely under high pressure.
Shouldered punches, such as those used to form bullet jackets from pieces of cut copper tubing, or to seat the lead core in a rebated boattail bullet jacket (which can have a tendancy to flow the jacket material forward unless a shouldered punch is used), are adjusted for projection length of the smaller tip section by loosening a locking nut on just below the head, and then turning the head relative to the outer sleeve (which creates the shoulder with its end). When the desired tip projection is set, the locking nut is secured again.
Because of the unusually high stresses on these parts, a properly built adjustable punch requires extensive heat treatment and is built of tough, highly resiliant alloys. The cost of making such a punch is about three times what it takes to machine a solid punch which has no adjustment. The point of positive return is reached when you need three or more different solid punches of the same diameter but with different probe or tip lengths. This might be the case if you were making your own bullet jackets in three or more lengths.
Also, if you want to use one hollow point punch to create a variety of depths of hollow points (not to be confused with open tips, which are simply more or less lead seated down inside the jacket, leaving an open space at the tip), then an adjustable HP core seating punch would be more economical than buying three or more fixed length (standard) punches.
The thinnest jacket that will allow enough sleeve thickness to withstand the pressure is usually about .025 inches. Jackets thinner than that may or may not provide for enough sleeve thickness to avoid folding, cracking or other failure under pressure. Fortunately, the problem seems to occur primarily with copper tubing jackets or very thick drawn strip jackets, where the sleeve is at least .025 and usually between .030 and .050 inches in thickness.
To summarize, the circumstances where an adjustable punch would be more desirable (and cost effective) include:
- Three or more lengths of copper tubing jacket (adjustable end flattening punch).
- Three or more depths of hollow cavity (adjustable core seat/HP punch).
- Three or more lengths of jacket used with RBT (adjustable shouldered CS punch).
The types of punches are:
- PUNCH-MA: For older -M dies (CSP-3 Silver Press press)
- PUNCH-SA: For current production -S dies (CSP-1 Series II press) up to .375 caliber.
- PUNCH-SL: For current production -S dies over .375 caliber.
- PUNCH-HA: For type -H dies (CHP-1 Hydro-press, CSP-2 Mega-Mite press)up to .375 caliber
- PUNCH-HL: For type -H dies over .375 caliber
The adjustable punches are not usually made for -R (reloading press) style dies, which have fewer uses for them since tubing jacket making kits and rebated boattails are not offered in the -R series. Also, the method of assembly of the -R external punches, with the attached button shell holder for a reloading press ram, interferes with the design of the adjustable HP and makes it less practical than in the dies built for Corbin presses.
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