Finning at the nose

[rvpilot76]

Got a new RCBS-309-200-SIL mold from Midsouth, and got to casting with it last week. I normally like frosty boolits, which means I cast hot; usually in the 800 degree range. I could not stop that mold from finning! I ran alloy temps from 700-800, and mold tems from 300 (where I like it), all the way down to 110 degrees. No change whatsoever. Mold faces are clean and flat (as best as I can tell), and it looks like the mold faces are coming together completely at the bottom of the mold. I am using straight wheelweight alloy, and I was bottom pouring initially. I switched to ladling, to see if that would help, but no dice. You fellas got a fix for me, or did I just get a bum mold? I've never ran into this problem before, so any insight you guys could give me would be greatly appreciated.

Thanks in advance,

Kevin

[405]

Have had it happen a few times with new molds. You've probably already checked for any small burr or piece of crud on one of the faces. So, just hope it's not warped :(

Besides that only one other possibility that I can think of and have seen it in a couple of new molds. Either there is a burr where the alignment pin (s) is pressed into the block. Or the corresponding alignment pin hole (s) on the opposite block is a tad small or has a burr on it's rim. Good light and magnifying glass might help inspecting. The last one doing that to me turned out to be the alignment hole rim was a little small/burred. I VERY CAREFULLY used a chamfer tool and touched the hole with light finger pressure. Solved it and allowed the opposing pin to fully engage the hole and maintain alignment.

[fourarmed]

405 is right. If it is finning, something is holding it open.

[NSP64]

I have a 243 RCBS mold that makes boolits that has propellers at the front.

[GSM]

As fourarmed said - something is keeping it slightly open.

Using a cold mould! Can you see a gap if you hold the mould over your eye and look at a strong light? Try it with and without the handles on it.

If there is a small gap, does it disappear if you squeeze the handles fairly hard?

Are there any burrs on the pin receiving holes?

Does changing (flipping) the handles make a difference in a gap?

Do the pour holes in the sprue plate look proportional to the bullet? If it's nor venting adequately, it MIGHT be pressurizing the cavity as you pour.

Some things that might be causing the fins.

[ktw]

I have a couple fo RCBS molds that will "spike" (lead in the vent lines) when the alloy is too hot. This usually happens when the alloy is much over 700 degrees. I run them at an alloy temp of 650 without any problems.

-ktw

[cajun shooter]

All the above answers are correct. The last 2 molds I received had burrs on the pin holes. I use a Dremel with the cratex polishing point and smooth them out. Problem fixed.

[rvpilot76]

I thought it might have been alignment pin holes and/or studs, and I checked them with a q-tip to see if it caught any of the cotton. I will deburr the holes and see if that makes a difference.

Kevin

[rvpilot76]

Well, I'm still getting finning at the noses, despite all the great advice I got here. The worst is right at the vent line at the nose meplat. I'll take a photo tomorrow and show you all what I am dealing with.

Thanks in advance,

Kevin

[Rick N Bama]

Kevin I bought a new RCBS 9MM-147 mold that did the same thing. I finally gave up & just sent it back to RCBS along with a note outlining the problem. They chose to replace the mold & the new one has given me good service. I suggest you do the same. RCBS is a good company & will do you right.

Rick

[KY_Camper]

Have you tried putting a touch of lube on the allingment pins? I had the same problem that a touch of lube fixed. I used some high temp anti-seize that I had but as i recall someone here had something that is supposed to work better.

[rvpilot76]

I've got Bullshop Sprueplate lube on the pins. I'm going to call Midsouth today to see if they'll exchange it for me.

Kevin