What is a core bonded bullet.? I've heard this term used by a commercial bullet manufacturer but not yet heard a custom maker use this term...
what is this??
thanks!
Kirk
Core bonding is a process that joins the core of the bullet to the jacket material.
There is a few ways to do it and most factory bullets are chemical bonded because that works into a mass production system well.
Most amatures use the solder process it is quite simple and requires few tools.
The process is based on melting the loose lead core in an unswaged bullet jacket in the presence of a soldering flux. Resulting in a lead core that is strongly soldered to the inside of the jacket.
Prepare a heat resistant block to support jackets during heating by drilling some holes into a fire brick or similar. Use a drill press so that the holes are nice and vertical. Holes should only be deep enough to support jackets and keep them vertical. Make holes slightly larger than jacket to allow for heat expansion. During use place extra bricks around the sides of the support brick to trap heat at the jackets. Make sure that bricks are placed on a flat level surface so jackets are infact close to vertical during heating.
Prepare jackets and cores as for normal swaging up to the point just before you would normally core seat. Wash out the inside of the clean jacket with a cotton tip dipped in Zinc Chloride flux ( Bakers flux) available from hardware stores . Then dip whole core into same flux using a set of large tweezers and place core inside jacket making sure cores are against inner base.
Then place jackets into support fire brick and apply heat on one jacket at a time with a paint stripper heat gun. Watch each lead core to make sure that the lead melts completely before moving on to the next.
On cooling a small hole will appear in the face of the lead core. This is normal and will be flattened down by the core seating punch.
Allow jackets to cool but while they are still slightly warm place them into a mixture of 50% CLR ( Sulfamic Acid (Household bathroom cleaner ))50% water or Medtech Solution ( medical instrument cleaner) to remove flux residue.
This is the only hard part of the process, getting the flux residue off.
There may be other better cleaners but don't use ammonias or amines as they harden brass.
Wear some protective gloves.
Agitate the mixture and scrub the surface of the lead core with a small brush if necessary, until clean.
Rinse off in hot water twice.
If jackets are still discolored then place in tumbler with treated walnut media and polish , or for a small batch polish them up by hand using steel wool .
Wash off media residue by replacing in solutions above for short time and then wash in hot water twice. Give a final wash in a fast drying solvent like Shelite ( liquid hydrocarbon). Place bullets on a tray and spread them out . Place tray out in sun until completely dry . Caution* Do not be tempted to use heat gun to dry bullets as you may melt the cores* If you are in a hurry you can use a hair dryer no closer than 12 inches.
Lubricate as required with a non detonating swaging lubricant ( 50% lanolin ( Wool Fat) and 50% Vaseline ( Petroleum Jelly). Heat and mix.
Carryout core seating as normal using a neat fitting punch that will not allow any side bleed of lead from the core.
Point form as normal. You will notice on point forming that a slight radius is formed at the junction of the jacket wall and base. Like a very small boat tail. This is because the core bonded bullet is a lot stronger and does not let this part of the core move much during point forming pressure on the base. So usually it takes a lot more pressure to flatten the edges of the base than to form the ogive. This will vary according to the length of ogive, jacket thickness etc etc.
It is not detrimental that I can tell and may even help down range ballistics as per a slight boat tail.
Improves bullet seating .
If you get core bonded and loose core bullets mixed-up then you can tell them apart by the larger radius on the base of the bonded bullet. This process is most suitable for bullets with shorter ogives say 8 caliber and under. Most big game bullets are the shorter ogive anyway. Having said that there is no reason why you cant core bond any style of jacketed bullet having a gilding metal jacket.
The melting of the cores anneals the jacket making it much tougher and resistant to fracture on impact.
Downside is that a softer jacket will foul a bit more. I molycoat mine anyway and that helps to cancel this out.
Core bonded bullets have a unique performance capability. This is the ability to open fast like a normal bullet but arrest that expansion as the expanding lead pulls at the core bonded section.
It works like this. During point forming a small section of unbonded lead is ballooned forward to fill a section of the ogive. It is still connected to the original core by the strength of the lead. On impact this front section can expand rapidly but as soon as the lead and jacket are stretched to a point where the core bonded section starts, this rapid expansion slows and a more controlled expansion continues . Retaining a high percentage of bullet weight and producing a nice even mushroom.
That’s about all you need to know, I hope it helps you make some great game bullets or whatever. I am very happy with the performance of core bonded bullets made with this process. Jacket thickness is not a big issue as you can make a good medium game bullet out of a thin J4 target style jacket.
Written by John Valentine 20 / 05 / 91 Copyright .
For the 105-108Gr., 6mms, you'll probably want 1.150" long jackets. RG
