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Draw Dies

Jacket Reducing Dies: Draw down a jacket

22 Rimfire Jacket Makers: Make free jackets

Bullet Reducing Dies: Draw down a bullet

Serrator/Draw Dies: Put serrations in a jacket

Expand/Trim Dies: Trim a jacket shorter

Two Kinds of Basic Draw Dies

Corbin builds draw dies for two general purposes, jacket reducing and bullet reducing. One is called the Jacket Reducing Die, catalog number JRD-1- (with -R, -M, -S, or -H suffix to show the kind of press it fits). The other is the Bullet Reducing Die, catalog number BRD-1- (with appropriate suffix letter). A jacket draw die or JRD has a punch which fits inside the bullet jacket (empty skin of the bullet). It can fit a piece of copper tubing (in which case it may have a shoulder to push on the edge of the tubing), or a closed jacket cup (no shoulder needed).

A regular draw die for jackets simply pushes a larger jacket diameter through a specially shaped hole so it comes out smaller in diameter, and longer. The jacket wall can be made thinner, or not, depending on the clearance between the punch and the die walls.

The amount of reduction that can be made depends on these factors:

Jacket wall thickness
Change in diameter
Material hardness/ductility
Original wall thickness run-out

The jacket wall thickness and material ductility will influence both the amount of force required to reduce the jacket, and the strength of the jacket base where the force may be applied before the punch simply breaks through the jacket. If the change in diameter is too extreme, or if the walls are too thick or the material too resistant to drawing, the force may be so great that the job simply takes more power than can be reasonably applied before bending the punch. If the material is too ductile, or brittle, or thin, and the change in size too great, the material will rupture with less force than it takes to finish the draw.

Therefore, the factors that make a given draw possible are complicated and may require some research and development work, unless the job has been done here before and the parameters already determined for it. Some draws may not be practical in a hand press, or, if the ID of the jacket is very small and the reduction large, it may not be possible to apply enough force without bending the punch.

5/8-24 tpi jacket drawing punch with -H adapter

In these cases, the draw may be accomplished in several stages, with more than one draw die, so that each step requires less reduction in diameter and therefore less stress on the material. Normal bullet jackets have walls that are from 0.020 to 0.050 inches thick, with the average about .026 and tapering to about .012 at the mouth. They are usually made of a 5% to 10% zinc, 95% to 90% copper alloy. With the normal jacket, a reduction of perhaps 50% of the original diameter per draw is practical. That is, a .308 usually may be drawn to .257 (or anything larger such as .284) in one pass. The brittleness of the material, its grain structure and state of heat treatment (anneal) or work hardening will determine just how far any given jacket may be drawn.

Jacket drawing is limited by another factor besides the jacket strength and rupture point. It is limited by the acceptable concentricity variation. When a jacket is pushed through a draw die, the punch which fits inside the jacket must be small enough so that it can pass through the tightest constriction in the die with the jacket around it. But this means that the punch will be smaller than the ID of the jacket before the jacket is drawn. Alignment of the punch to the exact center of the jacket will therefore be somewhat random, because the jacket can slip to one side as the punch and jacket enter the constriction area.

The issue of concentricity is one that directly affects the complexity, labor time, and cost of making a draw die. A simple die with just a constriction is relatively easy to build, but it provides reasonable concentric alignment only for fairly small reductions. A large reduction not only pushes the jacket off to one side as it goes through the constriction, but force material at the mouth of the jacket to flow so that one side of the mouth is much higher than the other. This visible difference is exaggerated when the bullet is brought to a small, open tip, and makes the bullet look very much "lopsided". These simple draws make jackets that work fairly well for lead tip and 3/4-jacketed bullets, because the jacket end can be a little crooked and not affect the flight if the jacket is not brought to a tightly closed tip.

For better appearance and performance with open tip rifle bullets, concentricity is improved by using a slightly more complex die that has a pre-alignment chamber for the jacket, starting and holding it very straight as it goes into the constriction area. This does not align the punch in any way but it insures that the jacket does not "tip" as it is pushed through the die, improving the concentricity over the basic draw die. Punches can be made of tougher steels, which tend to resist flexing but are more time consuming to heat treat. (See JRD-2 Draw Dies)

Corbin builds the simple JRD-1 for general purpose drawing, and the more complex JRD-2 for closer control of wall concentricity and for reducing the wall thickness while drawing the diameter down. The JRD-1 punch is a simple straight rod press fitted with threaded base base appropriate to the press ram, whereas the JRD-2 punch is from one piece of tougher steel either directly threaded into the ram or fitted to a 5/8-24 to 1-in x 12 thread base (for the -H presses). The difference in cost reflects the additional time for turning, polishing, and heat treatment with the tougher steel, as well as the extra time required to machine and lap the pre-alignment guide or "nest" in the JRD-2 die cavity.

If there is enough free ram travel (before the jacket engagement and reduction stroke), the punch can be made with a dual diameter. The larger, lower portion of the punch can engage the alignment chamber in the die before the jacket enters the drawing constriction (provided the length of the jacket is considerably shorter than the total press stroke). This gives the punch greater support and alignment with the die walls, and greatly improves the concentricity of the draw. Corbin JRD-2-H jacket draw dies for the larger -H type Corbin presses (CSP-2 Mega Mite, Hydro-Press, Hydro Junior) take advantage of the longer 6-inch ram travel of the large presses to provide more alignment pre-travel in the die.

Ultimately, the finest concentricity of drawn jacket is limited by the slight "spring" of the long thin punch. As the ID of the jacket becomes smaller, and the length of the jacket is made longer, the punch becomes more flexible even with an alignment section or sleeve surrounding the lower portion. This flexibility can cause the punch to wander slightly about the axis of the jacket during the draw. Most draw dies will accentuate any pre-existing eccentricity because the jacket wall which is thicker will force the punch to flex toward the other wall.

Corbin die-makers have developed a system that uses such massive alignment surface and length ratios compared to the draw length, that the system actually muscles the thicker wall material around and brings it back into greater concentricity than before it was drawn. In some instances, the benchrest grade drawing dies have taken cups with .002 or more run-out (difference in thickness from one side of the same jacket to the other side) and reduced it in one draw to less than 0.0005 inches. Then in a second draw, the .0005 run-out was reduced to less than 0.0001 inches.

Benchrest near-0 run-out style of draw die

Such reduction in run-out is impossible with conventional draw dies. In order to hold extreme tolerances between the alignment section and the bore of the reducing die, the die must be machined from one solid piece of material without being removed from the collet, and must be heat treated using extreme measures to assure alignment, such as using a sacrificial mandrel which is part of the die until it is nearly finished, then cut off and thrown away, leaving the actual die in perfect alignment during prior stages of manufacture. Naturally, the cost of building such dies needs to be balanced against the benefit of such extreme close tolerance draws. Corbin Benchrest Draw Dies are for building the ultimate in near-zero run-out jackets, but the benefit of such jackets is limited to world-class benchrest competition and a very few other high precision applications.

In most cases, a standard draw die, or the next step up (a commercial variation using a long-stroke press such as the Mega-Mite or Hydro Press), is more than adequate for target shooting, defense, and hunting applications. When one wants the ultimate in jacket run-out elimination, the procedure and tooling is available.

Jacket drawing dies generally are not quite so critical in diameter control as bullet draw dies. The jacket can vary several thousandths without any ill effect, since it will be sized by the swaging process. The critical parameter is concentricity, not exact diameter.

BULLET DRAW DIES

A bullet draw die works by pushing the finished bullet through a hole, supported by the base in most cases. It is sometimes more desirable to support certain bullets by the nose, and when this is better, it is suggested either with the order or during the testing and development stage (as soon as we know).

The BRD-1-R die fits into a reloading press. The punch has a button "shell holder" appearance, and snaps into the RCBS type T-slot ram. The die is 7/8-14 threaded and screws into the press top like a reloading press die. The BRD-1-S (which is identical to what would be a BRD-1-M so we don't make a separate -M type) fits into the S-Press, or the older Silver Press or Series II press. It can also fit any other Corbin press if you adapt it with the reloading adapter bushing and a 5/8-24 ram adapter. The BRD-1-H fits the larger Corbin presses, such as the CSP-2 MegaMite, the CSP-2H Hydro Junior, and the CHP-1 Hydro-Press. It has the additional advantage of a longer punch and a stronger die.

In general, use the reloading stroke on Corbin dual-stroke hand presses. Very long bullets may require a short helper punch or pusher rod behind the bullet after you push it as far as you can with the normal punch. If you should find that there isn't enough ram stroke to push a bullet through a die, most likely you have the press in the wrong stroke mode (short or swaging instead of long or drawing). Read the instructions again for your press, and note the way a Corbin hand press is changed from a short ram travel to a long ram travel by moving the ram pin to a different set of holes, and removing the knock out bar or the stop pin. (Sometimes people forget to remove the stop pin, and then the ram will not travel its full stroke in the long stroke mode.)

BRD-1-H

Bullet draw dies are not done absolutely "by the numbers" because different materials spring back by different amounts. Even the same brand of bullet made from a different lot of materials may have heat treatment, work hardening history, or other factors that affect the way the jacket expands after pressure from the draw die is removed, so slight differences in diameter will occur if anything about the bullet is different from the test and development samples.

For high precision results, we must have exact samples from the same lot of bullet you intend to reduce. Otherwise, we can only guarantee that the samples we use for testing will come out the correct diameter. Other bullets pushed through the same die may come out from .0001 to .001 inches different in diameter from our test samples. This is only basic physics, not a quality control issue. If you want the best precision, send samples and then stick with that particular bullet.

Each bullet draw die is hand made and tested to exactly the diameter you specify, down to 100 millionths of an inch with the samples used for drawing. No two bullets made from different lots, or certainly different brands or weights, are likely to come out precisely the same diameter. The hole we make in the die is not the diameter of the bullet. It is larger or smaller depending on the reaction of the materials, and is determined by testing and adjusting in the final stages of construction.

A BRD usually costs less than a swaging die set. The BRD will make very good bullets if you keep the reduction (difference between the original and final diameters of bullet) to .005 inches or less. While you may be able to reduce a larger amount, the jacket and core begin to separate inside, and the bullet jacket begins to take on a curve shape. Lead begins to spurt out the open end of the bullet, and the shank portion becomes very long in comparison to the ogive. The ogive is intercepted at a point which is increasingly closer to the tip as you continue past .005 inch reductions, until by .010 inches the bullet may be unshootable. This of course varies somewhat with the specific design and caliber of bullet.

The pressure needed to push a bullet through a hole that is smaller than about .005 inches less than the original bullet diameter becomes so great that the punch (which must pass through the hole as well) tends to push into the bullet base (or nose, on dies using a nose-pusher punch). The base material flows back over the punch, and can either shear off as it goes through the die or smear back as a thin sheet of metal. In any case, a reduction of more than about .005 inches is considered destructive and harmful to accuracy, whereas one of .005 or less generally works. There is no magic about the .005 limit. It is simply a point where most people find the bullets on the cusp of acceptability; some will find a bullet acceptable that we would throw away, and some will find even a bullet that the majority of shooters find reasonably accurate to be unacceptable, so the exact amount of reduction that gives satisfactory results is subjective.

However, with bullet draw dies, we guarantee only that the bullet we use for testing and development of the die will in fact be the diameter requested. No warranty is expressed or implied about the accuracy, appearance, or any other feature of the bullet after drawing. We simply do not know, and cannot know, until the bullet is fired in your particular gun and judged by your particular standards. At that point, our work has been done. Under those circumstances, we offer bullet draw dies. We recommend instead the bullet swaging die sets, because of the precision, weight control, design features, and other factors that are under your complete control with swaging, and are not with drawing factory bullets. But we understand the reasons people sometimes could justify a draw die and not the cost of a swaging die.

In nearly all cases, perhaps 999 out of 1000, our clients have been more than happy with the results of a bullet draw die. In about 0.1% of the cases, the bullets are not what the client expected. We hope that by explaining the limits of bullet drawing, even that 0.1% will understand what to expect. In most cases the bullet is nearly as good, or even as good, as it was before reduction, in regard to practical field accuracy. The less it is reduced, the more satisfactory it will be. A .357 reduced to .355 is nearly identical in accuracy. A .338 reduced to .323 is less accurate although still shootable. A .308 reduced to .307 is as good as it was before reduction, for nearly any practical use. In the laboratory some slight difference can be found. Shooting a world class benchrest competition with reduced bullets might put you out of the top ten, but shooting varmints or deer or even most high power matches would most likely not make any difference to you or the targets-- provided you stay within the guidelines and provide samples, then use those same bullets.

If you can stand a tolerance of plus or minum one to five ten thousandths of an inch, you can most likely use different lots and brands of the same diameter bullet, provided you don't mix completely different construction styles (such as the Barnes solid copper bullets and conventional Sierra Matchkings). If you use the sample bullet that was used to build the dies, tolerances should be very nearly zero, unmeasurable with any screw thread micrometer.

BRD-1-RC

Operating a bullet reducing die is simplicity itself: you put the punch into the press ram, screw the die into the press head, and push the bullets through using the end of the stroke (adjust so that you use minimum effort and just get one bullet completely through before another one encounters pressure against its base).

There are two kinds of bullet reducing dies, the BRD-1-x and the BRD-1-xC, where the x is replaced by either R, S, or H depending on the press for which the die is designed. The BRD-1 is for flat, dish, or cup based bullets where the base will support the force against a flat punch tip and not become distorted. The BRD-1-xC is for RBT or boattail bullets, or for faster operation with any bullet. It uses a punch with a spring-loaded sleeve guide to hold and support the bullet, so you don't have to do it with your fingers. The punch may also be machined to match the base, depending on how well the base tolerates the reducing force. BRD-1-HC

The special punch lets you quickly insert the appropriate bullet, remove your hand and stroke the press without fear of the bullet tipping over or falling off the punch. This means you can process bullets much faster than with the standard BRD-1. Also, the standard BRD-1 may not be appropriate for a boattail or hollow base, either because the base won't support the pressure unless the punch is machined to match it, or because the bullet will fall off the punch or be too hard to align without pinching your fingers!

See the Corbin Price List for current prices of the JRD-1-R, -M, -S, or -H, and the BRD-1-R, -M, -S, or -H dies. Draw dies come with simplified instruction sheets, and full details of operation are found in the Corbin Handbook of Swaging, No.8, and the book "ReDiscover Swaging", both available from Corbin.

Serrate/Draw Dies

A special kind of draw die is the Serrate/Draw Die or SDD-1- (-R, -M, -H). This kind of die puts shallow slits or grooves in the outside of a bullet jacket, so it will open faster on impact. The SDD-1 cannot selectively serrate a portion of the bullet that is in the middle of a parallel section: it serrates all of the parallel sides of the bullet at the time the jacket is pushed through.

SDD-1-S Since the ogive can be formed after the serrations are made, it is possible to have serrations on the curved portion of the bullet, all the way to the tip. It would NOT be possible to serrate the curved portion AFTER it has been curved in the point forming die, however. This die is also called a "Crown of Thorns" die, because it consists of a bullet-diameter cylinder with sharp cutter points positioned around the circumference, pointing inward and projecting an adjustable amount (from zero to perhaps 0.010 thousandths of an inch).

This process does not cut the bullet jacket through. It cuts a thin groove in the OD of the jacket, up to .01 inches deep. This groove then acts as a stress concentration point when the bullet impacts, causing the jacket to break open and peel back along the serrations, which are the weakest points in the jacket wall. Since the jacket is serrated before the core is seated (in most cases, although it is also possible to make a serrator for a seated core/jacket combo), the punch fits inside the jacket and does not touch the cutter teeth.

SDD-2-S You might use this draw and serrate die to make high fragmentation pistol bullets, highly frangible varmint bullets, or with low velocity rounds that cannot expand a normal jacket even with a large hollow point (or when the hollow point would interfere with operation of the gun). A discussion about your particular application is an important first step in getting the correct form of SDD-1. Subsonic bullet designs often include serrations, a large hollow point, and a blunt round nose with a RBT style base.

SDD-2-H A second kind of Serrator Draw Die is the SDD-2-S or SDD-2-H. This kind of die fits into the press ram, and accepts a jacket with a seated core in it. The jacket is pushed open end first into the die using a fairly conventional punch that fits into the floating punch holder. The jacket is serrated only at the end, not full length. It is ejected back out of the die on the return stroke of the press. The ejector fits into the jacket mouth and is a loose fit into the die itself. The external punch fits the kind of base on the jacket, being flat or rebated boattail depending on the design of bullet.

The SDD-2 is generally used when you only want faster opening without fragmentation, or with a high retained weight for the rear portion of the bullet. It is used in combination with bonded cores, hollow points, tapered or heavy based jackets, or other means of making the bullet stay together at the rear while expanding faster at the front.

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