Finning on Mould

[standles]

Guys:

I got a "problem child" mould from a friend. It is a dbl cav 325gr 45-70 RCBS.

I have lapped it out since it was undersized (.456 ) but noticed its affinity to fin the bullets nose and wisker at front vent lines.

IN holding it up to a light I can see light through the middle of the mould when closed. If I exert a good amount of pressure (more than I would want to do regularly while casting) I can mitigate it somewhat.

I assume my next job will be to lap out this bow on some plate glass but that will diminish or remove the vent lines. Also the two aligment pins will be in the way on one half. I assume that are pressed in but how would I get them out without disfiguring them or destroying them?

IF any of you have gone down this road please let me know how to proceed and if your efforts were successful.

Steven

[BABore]

You should be able to drive the alignment pins out with an aluminum or brass rod and hammer. This will keep you from damaging them. Drive them from the cavity side, toward the outside of the block half. It is very possible that a burr around the pin base is keeping the block halves apart. Check for light again after you get the pins out. You may have to put a slight chamfer on the holes, then stone them to get things right. When you reset the pins, they should only protrude far enough so the blocks don't wiggle. Any more and you may create another gap. You might even just try tapping them in a hair and check for light and wiggle. May cure it right there.

[Ricochet]

Problems I've had with moulds not closing fully and producing finned, out of round boolits haven't been from mould faces not being flat. They've been from something holding the blocks apart, usually either lead, residue from burnt mould lube, dirt, etc. Check the cavities the alignment pins go into closely and make sure they're clean, and that the pins are clean and not protruding too far from the blocks. And of course that the block faces are clean.

[beagle]

I'd say the best place to start would be to reset the alignment pins. That will probably cure the problem. Don't mess with the mould half faces right now. Anything on them would be readily apparent./beagle

[montana_charlie]

but noticed its affinity to fin the bullets nose and wisker at front vent lines.

If I exert a good amount of pressure (more than I would want to do regularly while casting) I can mitigate it somewhat.
The advice you have received is good information...well worth checking out.

But your description (above) seems to say that your mould closes at the back (the side toward the handle hinge) but not at the front...and, squeezing can make the open side close a little more.

That CAN be caused by interference between the mould handle slots, and the handle jaws. When this kind of interference is found, it usually exists at the 'back' of the mould...much like your situation. This most usually occurs when the brand of the mould and the brand of the handles are not the same.

The slots in the mould-half have three sides. It is the 'bottom' of the slot (when the block is lying face down) that interferes with the jaw on that side...and the interference occurrs at the rear corner of that 'slot bottom'.

You can bevel the mould slot corner, or notch the handle jaw, to remove the interference.
CM

[Wicky]

Had the same thing happen to a CBE mould using Lee handles. The solution was to lengthen the angle on the inside of the mould handles to allow the mould blocks more room to rotate.

[standles]

Thanks for all the replies.

I will be back in town tommorrow and give them a look see.


Much appreciation,
Steven

[Dale53]

It is not uncommon to have a burr surrounding the alignment pin opening. It happens when the blocks are closed with too much "enthusiasm" when hot. Careful work with a needle file can solve this. Emphasis on "Careful"...

Dale53

[mooman76]

If you are using the Lee 6x handles with the RCBS mould the handles do that sometimes. Yu might need to file the pin holes in the handles a little to get a better fit. I tap my lee moulds with a light weight plastic hammer when I close them and it helps them close tighter.

[shotman]

some have hit on your problem check to handles to see if they are letting mold close true if it does not close square together then the line up pins will bind like tring to put a football through a round hole shotman

[standles]

Ok here is the follow-up diagnosis....

I checked the faces of the mould halves with a magnifier and found no burrs or errant buildup.

I backed the alignment pins down and slightly chamfered the holes to ensure no burrs there.

I put the mould halves together (without handles) and still saw a light gap.

I borrowed a machinists straight edges and using that light started working along each mould face.

I FOUND IT!

Seems the previous owner had taken a center punch and put a dimple on the nose of one cavity to mark it. HE apparently got to close to the edge of the mould because there is a minute bulge at that location. So a little judicious stoning to the high point should solve the problem or at least I hope it does. That is a chore for tonight if I get a chance.

Thanks for al lthe pointers and if this works I will let ya know. If it doesn't you can read about the man running down the street foaming at the mouth, pulling hair and cursing RCBS :)


Steven

[Ricochet]

Great!