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.he CHAPTER 3 CORBIN HANDBOOK AND CATALOG NO. 7, PAGE #

                            ABOUT BULLET JACKETS
        Bullet jackets are the skin of the bullet.  They are what makes it 
   possible to achieve velocities over 4,000 fps and still have no fouling 
   from  melted  lead  in your barrel.   But besides elimination  of  lead 
   fouling,  the jacket has another important job.   It helps control  the 
   terminal performance of the bullet.
        Bullet jackets are available from Corbin in packages of 250 or 500 
   jackets,  depending  on the caliber and length.   Popular calibers  are 
   stocked in certain lengths that are most useful.   Not all calibers  or 
   lengths are available directly.  Some you have to make yourself, by re-
   drawing a more common size.  This is done with a Corbin JRD-1 draw die.
        Other  calibers  can be made from copper,  brass,  or  even  steel 
   tubing.   A  reloading  press can only use the  commercially  available 
   drawn gilding metal jackets,  which range from 0.017 to 0.032 inches in 
   thickness depending on the length and caliber.  The Mity Mite press can 
   form jackets from 0.030 inch thick copper tubing (hard drawn,  straight 
   tubing,  not the soft coiled type).  The Mega Mite can handle tubing in 
   0.030  and sometimes in 0.049,  depending on caliber.   The Hydro-press 
   can  handle anything,  from the thinnest copper to the  thickest  steel 
   walls  (typically 0.050 steel or 0.065 brass is the heaviest  practical 
   jacket wall, beyond which you may as well swage solid copper rod).
        From .30 caliber rifle down,  it is both easier and cheaper to use 
   commercially made jackets and either use them as is, or redraw them for 
   smaller or longer jackets.   Jackets can expand considerably during the 
   core  seating  operation,  to become larger in diameter.   Jackets  for 
   bullet  swaging in Corbin equipment are all made several thousandths of 
   an inch smaller than the final bullet diameter,  so you can expand them 
   upward for a perfect, tight fit on the core.
        This  is one reason that it isn't feasible to pour hot lead into a 
   jacket and make a jacketed bullet.   The pressure of swaging is  needed 
   to  expand  the assembly to the right diameter inside a  die.   Another 
   reason  is that the hot lead would shrink away from the  jacket  during 
   cooling, leaving a loose core that would not stabilize in the rifling.
        In  the calibers from .309 to .338,  it is possible to use regular 
   .30  caliber jackets.   Special techniques to expand the jacket  evenly 
   include seating the core in two short sections,  so that the base  will 
   form properly.   This is done on the .338 and .333 calibers,  but isn't 
   necessary  on the .311 and .314 sizes.   Using this method,  it is even 
   possible to expand a drawn .22 Magnum fired case into a nice 7mm (.284) 
   bullet!   It  works best with a rebated boattail die set and with three 
   or four short cores seated on top of each other, one at a time.
        The  best known jacket among bullet-makers is the .22  Long  Rifle 
   case used for a .224 or a .243 caliber jacket.   Corbin makes a die set 
   called  the RFJM-22 that turns these rimfire cases into  straight-sided 
   jackets of the proper diameter.   Vernon Speer,  Harvey Donaldson,  and 
   Fred  Huntington  were a few of the well-known experimenters  who  used 
   this  method  in the late 1940's.   Speer and Huntington both  launched 
   major businesses from this beginning.  
        The  process had flaws in those days,  because rimfire cases  used 
   mercuric priming compound.   This left the jackets weak and brittle, so 
   they  fouled the bores and often came apart  on  firing.   Today,  non-
   mercuric  priming is used in rimfire cases.   The jackets you can  make 
   for yourself not only are as good as any you can buy for most practical 
   purposes, but they are free!
        The  disadvantage  of making rimfire jackets is that  the  bullets 
   have  very  thin skins -- typically under 0.015 inches  -- without  the 
   thick taper toward the base which commercial jackets have.   This means 
   that  they are excellent for varmint shooting,  because if they hit the 
   ground they normally blow up and do not cause a ricochet.  But they are 
   not  suitable for high velocity (beyond about 3500 fps they blow up  in 
   the air), nor are they suitable for serious game hunting.
        You  may  be surprised to learn that the  commercial  standard  52 
   grain bullet has a jacket that matches the length of the drawn .22 Long 
   Rifle  case.   This  is because the first .224 commercial bullets  were 
   made  from  such cases!   When bullet makers switched  to  drawn  strip 
   metal, they kept the traditional length.  Thus, you do not need to trim 
   your  home-made  jackets  or make excessive weights of bullets  to  use 
   them. 
        The  jacket  material  is normally  either  commercial  bronze  or 
   gilding  metal.   These alloys are 10% zinc and 5% zinc,  respectively, 
   with the balance of copper.   The zinc is for strength and anti-fouling 
   characteristics.   A  rimfire  case  is about 30%  zinc.   It  is  more 
   brittle,  but also less likely to foul the bore at normal  speeds.   By 
   annealing  the  case,  you can make it just as ductile as  the  regular 
   jacket.
        A  6mm  (.243-.244) bullet jacket can be made from the  fired  .22 
   case  (a  Stinger or other long case is best).   The head  is  smoothly 
   drawn  off,  leaving a diameter of about 0.219 inches at the end.   The 
   body  of the fired case is about 0.225 inches in diameter.   A  special 
   punch with a flare or bottleneck,  like a bottleneck cartridge, is used 
   inside  the case.   The jacket becomes slightly longer as it is  drawn, 
   and  this lengthening forces the mouth partly over the tapered part  of 
   the  punch.   It is this tapered mouth that lets you seat a  lead  core 
   into  the undersized jacket and expand it to full .243 size during  the 
   core  seating operation.   The flared mouth seals the die against  lead 
   leakage and makes the jacket expand perfectly. 
        The  .22  WMR case takes a different die (a special type of  JRD-1 
   die  is used) to make a long 6mm jacket.   By careful  manipulation  of 
   core weights and seating technique,  you can coax this jacket to become 
   a .257,  a 6.5mm,  or even a 7mm bullet!   This isn't something for the 
   beginner  to try,  but once you have mastered the basics,  it is fairly 
   easy to learn.
        Bullet jackets have different wall thicknesses,  not only  between 
   different  calibers  and  makes,  but  also  within  the  same  jacket.  
   Commercial jackets have a taper, to control expansion.  This means that 
   when  you seat the lead core into the jacket,  the core has to be small 
   enough to fit easily into whatever jacket you are using.   If you buy a 
   set  of dies that is made with punches for a certain jacket,  and  then 
   change to another jacket (such as going from a commercial drawn  jacket 
   to  a  copper  tubing  jacket),  you will probably  need  to  obtain  a 
   different core seating punch.  
        The core seating punch fits inside the jacket, rather than the die 
   itself,  whenever  you want bullets with the lead seated down past  the 
   jacket mouth.   (Bullets with large lead tips,  such as semi-wadcutters 
   and  lead round nose bullets,  are made using a core seating punch that 
   fits  and  seals pressure against the die wall instead  of  inside  the 
   jacket.)  If you change from a 0.020 inch wall jacket to one with walls 
   of  0.050  inch thickness,  then you need a punch that is  considerably 
   smaller in diameter to fit the new jacket.  When you order dies, either 
   let Corbin supply the right jacket to fit them, or send a sample of the 
   jacket  you want to use.   If you want more than one  jacket,  remember 
   that you may need more than one core seating punch.
        The other part that you may need for different jackets is the core 
   swage  die.   Core swage dies make the core the right size and  weight, 
   starting with an undersized piece of lead.   Reloading press dies don't 
   use a core swage for technical reasons.   Special swage presses  almost 
   always  use die sets that can have a core swage as the first die of the 
   set.   When you order a set of dies for jacketed bullets,  the diameter 
   of the core swage die is important to the diemakers.   The core that is 
   produced  must  be small enough to fit inside whatever jacket  you  are 
   going to use.   If you later add copper tubing,  or change to a thicker 
   wall  jacket  (such  as drawing down a larger caliber to get  a  longer 
   jacket for a heavier bullet),  it may require another core swage die of 
   smaller diameter.
        The  right size of lead wire or core mould for a  certain  caliber 
   depends on the jacket you plan to use.   Most standard jackets that are 
   available  from Corbin take standard,  off-the-shelf diameters of  lead 
   wire and core moulds.  If you furnish your own jackets, you may need to 
   send  samples to get a special size made to order.   Core size for  the 
   jacket  is  not terribly critical:   as long as the core fits  and  the 
   weight  is  about right without being so long that the core sticks  out 
   the die mouth, you can use any size.
        One exception is that your core shouldn't normally be a press  fit 
   into the jacket,  so that it traps air in the bottom.  The short, thick 
   half jackets for .38 caliber sometimes fit a bit snugly on the standard 
   core,  but  they  don't cause any problem.   It is  the  long,  tapered 
   jackets  of larger caliber handguns and of rifle bullets that create  a 
   potential problem with too snug a core.  
        The  problem  arises  when the core fits so tightly  that  air  is 
   pushed  into a highly compressed disk at the bottom of the jacket.   If 
   the  bullet  is  finished with the jacket brought around  the  nose  or 
   ogive section,  you don't notice any problem.  Accuracy is usually good 
   because the air is normally quite highly compressed and centered rather 
   well.   But if you make a semi-wadcutter style bullet (and by that,  we 
   in the bullet-swaging field refer to ANY style of nose,  be it round or 
   flat,  hollow or pointed,  so long as the nose is entirely made of lead 
   projecting from the jacket, and the jacket is NOT curved at all to lock 
   the  core in place),  then the trapped air can expand when the  bullets 
   are brought into the hot sun.  Sometimes, the cores will pop out with a 
   loud bang and jump harmlessly across the room!  
        The answer is to use a core that slips to the bottom of the jacket 
   without force.   Or, if you want to use a core swage die that is nearly 
   but not exactly right,  you might want to have the die-maker machine  a 
   special  internal  punch  with a cavity in the shape of a  boattail  or 
   Keith nose in its end.   The cavity would form a mirror image of itself 
   in the lead core,  so that a section of the core would then fit  nicely 
   into  the bottom of your tapered wall jacket without trapping any  air.  
   This  technique  lets  you  use the same core swage  die  with  several 
   calibers  and  with  several different styles of  jacket  in  the  same 
   caliber.
        The right core mould for heavy wall tubing jackets is much smaller 
   in  diameter than the right core mould for a standard drawn  commercial 
   jacket.   In fact,  the next smaller caliber of mould is normally used.  
   For  instance,  a  .30 caliber core mould might be used with  a  tubing 
   jacket  bullet  in .358 caliber,  whereas a .38 caliber mould would  be 
   used  if  you were to make commercial jacket bullets  with  those  same 
   dies.   When  you  order,  we supply the size of equipment  needed  for 
   standard popular jackets that we stock unless you specify otherwise, or 
   unless we know that tubing jackets are going to be used.
        Bullet jackets can make a wide range of weights even with the same 
   length.   The  exact weight range for any given caliber  and length  of 
   jacket depends on the ogive shape and base shape, as well as the degree 
   of  hollow  point  or hollow base and the lead density  used,  and  the 
   thickness of the jacket.  There is no single "right" weight for a given 
   jacket  because of all these variables.   But that means  you,  as  the 
   bullet-maker,  can  manipulate  the variables and produce all kinds  of 
   different weights using a limited stock of jackets.
        For instance, in the .44 caliber, a 0.54-inch long drawn jacket is 
   very  popular  with shooters who have 3-die sets,  such as  the  FJFB-3 
   type,  to  make bullets with the jacket curved around  the  ogive.   By 
   adjusting  the  amount  of lead used in the jacket,  you can  make  any 
   weight  from 180 to 250 grains with this jacket.   The lighter  weights 
   have  open  points,  and the heavier weights have more  and  more  lead 
   exposed at the tip.
        The  bullet-maker  who  uses a semi-wadcutter die  limits  himself 
   somewhat on the range of weights possible with a given jacket, since he 
   cannot take up any jacket length by curving jacket material around  the 
   nose.   He  can,  however,  change  the  amount of  nose  by  selecting 
   different  punches,  or  change  the amount of lead used  by  selecting 
   hollow point or cup base punches and adjusting how far he presses these 
   into  the die.   Then,  he can follow with the regular Keith  or  other 
   semi-wadcutter type of punch to shape the lead that is moved forward by 
   the hollow point punch. 
        This  technique lets the bullet-maker adjust weight even on  semi-
   wadcutter  style bullets with the same jacket length and still have the 
   same amount of lead showing!   A technique not widely known is the  use 
   of  ordinary  cornstarch  as a filler in the base of  the  jacket.   By 
   placing cornstarch in the bottom of the jacket and seating a lead  core 
   over  it,  you can produce very high velocity,  light weight bullets in 
   jackets that everyone else thinks only make heavy weight slugs.
        In  the .25 ACP caliber,  you can make jackets from fired  shotgun 
   primers  using  the SPJM-25 die set.   This kit lets you push  out  the 
   anvil  and cap,  and draw the top hat battery cup into  a  smooth-sided 
   jacket for a 45-50 grain .25 caliber bullet.  Jackets for sub-calibers, 
   such as the .14,  .17,  and .20 caliber, can be made from ordinary .224 
   commercial  jackets using three drawing dies.   The jackets need to  be 
   annealed  by heating to a dull red briefly,  so that the bottoms  won't 
   crack out when you draw them to .14 caliber.
        Dies that use larger caliber jackets, such as the sub-caliber draw 
   dies,  can  be made with a pinch trim punch so that surplus material is 
   pinched off as the jacket is drawn.   In order to pinch trim a  jacket, 
   there  must  be a reasonable amount of reduction taking place.   It  is 
   difficult to pinch trim a .38 jacket being drawn to .350, for instance, 
   because most .38 jackets begin at .3545 diameter.   That doesn't  leave 
   enough  difference for a pinch trim punch to work.   But drawing from a 
   .308  to a 7mm,  or from a 7mm to a 6.5mm,  leaves plenty of metal  for 
   pinch trimming to any desired length.
        You  don't  have  to use a jacket.   Many  handloaders  don't  yet 
   realize that bullet swage dies can be used with or without jackets, and 
   that a swaged lead bullet can be made faster,  more precisely, and with 
   far greater control of weight and style than a cast bullet.   The  same 
   dies  can be used for jacketed bullets or lead bullets.   (This doesn't 
   necessarily work in reverse:   if you buy a LSWC-1 lead  semi-wadcutter 
   die,  designed just to make lead bullets,  it won't make fully jacketed 
   bullets  because the bleed holes in the side of this die would then  be 
   covered by the jacket.) 
        Lubrication  on a swaged,  smooth-sided bullet is accomplished  by 
   changing  from  Corbin Swage Lube to Corbin Dip Lube.   Dip Lube  is  a 
   liquid  wax  that is applied to the core before swaging a lead  bullet.  
   The  pressure of swaging forms a hard,  tough film of wax all over  the 
   bullet.   The wax doesn't melt or affect the powder like bullet greases 
   do.  Since it covers the whole bullet, no lead is exposed to the air or 
   to the bore without having some lube between the bore and the lead.  
        Naturally,  this "liquid jacket",  as some people call it, doesn't 
   stand  up to the torque and heat of high velocity firing like a regular 
   jacket  would.  It does serve well for most shooters using loads up  to 
   1,200 fps,  and cuts the cost of shooting by eliminating the jacket  as 
   well  as speeding up the whole bullet-making process.   Corbin Dip Lube 
   is  available  in  pint cans or gallons.   A  sample  2-oz.  bottle  is 
   available as well.
        Re-forming  jacketed,  factory  or military surplus bullets  in  a 
   standard swage die (the point forming die,  usually) is also  possible.  
   There  are some cautions and limitations.   The bullet must be  smaller 
   than  the  final  diameter desired,  because you cannot expect  a  .308 
   bullet  to fit easily into a .308 diameter hole and eject easily  after 
   reforming.   It should be a 0.3085 to 0.3090 inch die in order to use a 
   .3080 inch diameter bullet for reforming.   Also,  there are some minor 
   problems  with  lead coming forward out the nose of a  finished  bullet 
   when you change the ogive shape to reduce the total internal volume.  
        But, on the other hand, we have made hundreds of single-die swages 
   that turned rather inaccurate military surplus bullets into soft points 
   of  very  good accuracy simply by swaging them backward,  so  the  base 
   became the nose and the pointed nose became a solid base!  And in other 
   cases,  we  have made 5.56 and 7.62 mm bullets shoot twice as  well  by 
   simply  bumping them up half a thousandth of an inch while making their 
   open bases more perfect and even.   These transformations are quick and 
   easy  when they can be made to work with a standard die.   I would  not 
   recommend  putting a lot of money into tooling specially built  for  it 
   unless you have a tremendous number of surplus bullets to reform.  
        Bullet  jackets  can be made that have partitions,  variations  in 
   thickness (selective heavier base sections),  completely closed  bases, 
   solid  copper  bases,  and multiple jackets stacked inside each  other.  
   Most of the heavy duty jacket making,  using copper or brass tubing and 
   such styles as the partition or H-mantle, are done on the Corbin Hydro-
   press.   Hand presses and dies made for them do not have the ability to 
   produce or withstand the extreme pressures used.  Within a more limited 
   range,  however,  you can still make exotic jacket designs by using the 
   telescoping  jacket idea:   putting smaller calibers inside  of  larger 
   ones is a very effective way to control performance.  
        A  thorough discussion of bullet jackets can be found in the  book 
   "REDISCOVER SWAGING",  and the various technical bulletins published by 
   Corbin  Manufacturing  have  further details on  making  tubing  bullet 
   jackets,  rimfire  cases into jackets,  and even the use of fired brass 
   cases as bullet jackets.
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