The Core Swage (CSW-1) is your (optional) starting point, for precision weight control, in any die set...
The Core Swage Die (CSW-1) accepts a cast core or cut lead wire of slightly heavier weight than desired, and adjusts its diameter and weight precisely. Core Swage dies typically are used to prepare the core for insertion into a bullet jacket, although for high precision lead bullets a core swage may be used to pre-adjust the lead weight and shape into a cylinder prior to reshaping in a core seating die.
These two steps can be combined in a LSWC-1 Lead Semi-Wadcutter die, which looks like a core swage die but forms the bullet base, nose, and final diameter instead of just preshaping the core. (For die ID markings, click Die Code).
Also, a lead bullet with a smooth ogive curve can be made in a combined core swage/point forming die called the PF-1-SB or PF-1-HB. This is a point forming die with bleed holes and a synchronized pressure sealing ejection, often used to make high precision airgun pellets and muzzle loading slugs. But for swaging jacketed bullets the CSW-1 core swage is universally employed as the first step.
Every set of dies normally includes the Core Swage Die, as the first die. You can choose not to purchase a core swage die, if you wish. The advantage of the core swage is that you can adjust the weight of the lead slug or core that you have previously cast or cut from a roll of wire, and make it far more precise.
The core swage die extrudes a small amount of lead through tiny bleed holes, so that the core becomes the exact weight you want. The core also is formed with clean, flat ends and a cylinder shape, to fit neatly into a bullet jacket (or the next die, for lead bullets). The flat ends help guide hollow point punches straight, in the following stages. Cutting a wire core leaves a shear angle on the end, which can drive a pointed punch off center. Without a core swage die, you may need to first press the end of the core flat with a flat punch, in the next die, before using certain other shapes of punches.
Core swage dies, like all swages, need to have a larger diameter hole than the lead you intend to put into it. Never force a larger piece of lead into a smaller die! It doesn't work. The diameter of the core swage will depend on the next step. If you are making a jacketed bullet, the core will need to fit easily into the jacket. The jacket may have thick or thin walls, so the core will probably need to be smaller for a thick-walled tubing jacket than a thin-walled commercial jacket. If you are making a lead bullet using two or more dies in sequence, the lead core can be much larger than it would be for the same caliber of jacketed bullet. For more info, click Core Size.
About Weight Control...
The only way a core swage die can give you consistent precise weights is if you allow the ram of your press to reach the same exact position for each core made. If the ram is raised part way one time, and all the way another, then the volume left in the die, between the top and bottom (external and internal) punches will vary on every stroke, leaving various volumes of lead in the die. The goal is to always leave the same volume between the punch ends, so all the surplus lead is extruded out the bleed holes, leaving a precise length of core in the die.
To insure constant weight, always make sure the core is 3-5 grains heavier than you need, before it is swaged. Then bleed off this surplus amount to make sure none of the cores come out lighter. Any core that does not bleed of some amount of lead, then, will be too light and can be instantly detected by the lack of resistance on the press. The ram must stop at the same point.
The best accurate stopping point is the physical end of the stroke, because the press cannot possibly go any further than this. If you set up the punch holder position, in the press top, so that you do all your core swaging as the press reaches the top limit of its travel, then the cores cannot help but come out the same length, and thus the same weight and volume.
As a further refinement, you can carefully control the length time that the press remains at the top of the stroke. Lead flows continually under pressure, so it will tend to "creep" under low pressure. If you jerk the ram rapidly up and down, your cores will vary because you interrupt the flow while it is at the greatest point (but not precisely there). If you press, hold a few milliseconds, then lower the ram, the cores will be more consistent in weight because the lead has had some time to slow down its flow before being interrupted.
The core swage die is also a percentage of difference device: it continually improves the weight control percentage as you re-swage the same core, because the core starts from a more consistent point and the slight bleed off that results is a more consistent amount as a result of the more consistently developed pressure. Thus, if you are extremely paranoid about weight variation, swage all your cores twice or three times, taking off 3-5 grains the first time, then 0.4 to 0.6 grains the second time, and finally less than 0.1 grains the last time. Does this amount of work translate to that much tighter groups? Probably not...weight control is far more important to handloaders than it is to the bullet trajectory or group size.
A weight variation of 5 percent (of total bullet weight) would cause enough variation in trajectory and burn rate to be a minor problem to a benchrest shooter and hardly any problem to a high power match shooter or game hunter. A variation of 1 percent (of total bullet weight) would be about as good as anyone would every need in practical terms, world class accuracy being possible if all else is in that class. A variation of 1/2-percent of total weight is beyond the stated accuracy of most scales and other instruments in any case, and is so precise that it no longer matters. Anything better is an exercise in the old syndrome that says "If your only tool is a hammer, every problem looks like a nail".
This tendancy to make every problem a weight problem is because the one tool nearly every handloader has, which is capable of 1% or maybe even 1/2% of full scale accuracy precision, is a powder scale. Certainly if the weight variation is caused by an eccentric jacket or air bubble in the core, then the bullet will not be balanced as well as it could be, and a small variation in weight from this cause would result in bigger groups. But if the same variation in weight is concentric, and only caused by more or less core length, then the effect on group size is negligable in ranges of variation of less than 1 percent of the bullet weight.
Note that we have only talked about percentages of total weight, not grains. Grains don't matter: percentage does. If you shoot a 1000 grain artillery round to pin-point accuracy, how much is a 1 grain variation? It is plus or minus 1 out of 1000, which is 0.001 or 0.1 percent variation. Does this have the same affect on trajectory as a 1 grain variation on a 20 grain .17 caliber bullet? (The 1 out of 20 ratio is 0.05 or 5 percent of the total weight.)
Certainly not! Does 10 grains on a cruise missile make any difference? So how do we decide how many grains variation is important? A good rule of thumb is that a concentric variation (meaning, it comes from more or less material in length, rather than inclusions or other off-center variations in the material) of 2% or better is fine for hunting, 1% or better is excellent for most target shooting, and 1/2% world class benchrest level.
What Size Core?
The core diameter from the core swage die must fit into the jacket you plan to use. And the lead wire, or core mould, needs to make a slug with a diameter that goes easily into the core swage die.
The external punch is marked with "S" to indicate that it fits a core swage die. The diameter of the die is also marked on the punch, rather than the caliber (because one diameter of core swage might be used with several calibers).
The core swage internal punch is also marked with "S" and with the diameter of the die bore (which is the same as the core diameter produced by this die). Note that core swage dies have bleed holes in their side to allow adjutment of the weight, and the internal punch must not cover these holes when the ram is raised.
The core swage die has an "S" and the diameter marked on its mouth. The illustration is of a type -S die (which fits the S-press, discontinued Hydro-Mite, and earlier Series II Corbin press). There are also type -R (for reloading press), type -M (for older Corbin and SAS presses), and type -H (for Corbin Mega-Mite, the discontinued Hydro Junior, and Hydro-Press systems).
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