Ok so after having a .308 diameter bullet blow up on the spine of a feral hog last year, and failing to kill the animal - I have started using bonded core bullets. Not to mention when I was sighting in my new loads - I recovered some of the bonded cored bullets that had been shot at bricks .... perfect mushrooms - figure bone won't be much trouble then.
Ok now onto what were discussing ....
I have spoke with Dave Corbin extensively about this issue. He specifically said to use regular flux and to avoid the rosin flux. Don' know exactly why he instructed me to do that, but I figure he's made a few bullets in his lifetime. So regular paste flux is what I use.
I apply the paste flux by dropping the cores into the container of flux and then just pulling them out. There is plenty of flux on the cores so when they are inserted into the jackets it gets where it needs to be. It's a little messier than other methods, but it is very quick and easy.
Next is the heating phase. I put all the jackets into a block of aluminum that supports the jackets with cores vertically. I heat the block of aluminum with my propane torch and then pass the torch over all the jackets individually. You do not want to heat the jackets to quickly or all the flux will burn up before the lead has a chance to liquidize and bond. Heat them up slowly and keep the heat on until the cores no longer bubble. ***WARNING*** The vapor that is let off during the heating of the cores is extremely corrosive. It will rust anything metal near by; so do it somewhere safe.
Onto cleaning the bonded jacketed cores. I use Birchwood Casey's case cleaning stuff. It is a citric acid and does not give off an odor. It cleans the jackets really well and does it quickly. I use my sonic cleaner to do the work. Dave Corbin also said that this is a VERY important step because the residue that is left on the cores/jackets from bonding will transfer to the swage dies and rust them as well if care is not taken. He recommends that you wash your dies after working with bonded cores.
On a side note - I was cleaning some cartoon bullets that I made out of 5.7x28mm brass the other night. I forgot to take them out after the machine was done and left them overnight. When I got them out the following morning - they looked just like copper jacketed bullets. There wasn't a hint of yellow and there was no pitting or rough spots on the jackets. They were nice and smooth and you couldn't tell they were not made from copper jackets if there wasn't the case head.
Anyway .... hope this helps you all since we are discussing bonding cores. Bonded cores are worth the trouble to me .... when hitting bone it's important to me for the bullets to hold together and finish the job they started.
Sarg