fins

[jcw1970]

I'm pulling my hair out. I have a new rcbs 270-130 I'm casting and I'm getting a small fin on the nose. I've checked the vent lines and they are fine. pins line up fine. I'm using a Lyman Mag 20. I've tried to vary the speed of the pour thinking it was coming in too fast and that didn't help. any ideas?

[waksupi]

Too much tin, perhaps?

[Bret4207]

While unusual, it is possible the blocks have a very slight warpage that leaves enough space for a fin. More likely is something- even a tiny burr- holding the blocks apart. Try scrubbing the block faces with 4/0 steel wool and make sure the pin holes are clear.

[WHITETAIL]

jcw1970, The best advice I can give you is.
Take the mold and push out the pins.
then take a good flat stone and rub the faces
flat.
this will show if the mold is flat or warped.
This will also take off any burr you might have.:killingpc

[The Dove]

You aren't alone my friend.... I gotta a .452 that has me pulling my hair out as well. Same problem as you are having but mine is a Lee 2-cavity mould.

The Dove

[Ben]

jcw1970 :

Before you panic...........try ladle pouring.

The volume and pressure of alloy from a bottom pour can be a good thing or a bad thing...depends on the individual characteristics of a mold. " Fins " can be caused by alloy that is too hot and under too much pressure.

I have several molds that don't respond well to a " pressure pour " from a bottom pour furnace.

They cast well & WITHOUT fins when I ladle pour with about 1/2 of the ladle full of alloy.

Wouldn't take you long to see if my suggestion has merit.......

Ben

[GP100man]

smoke the vent lines a little& see if it lessens the fins.
ultimately the blocks will need trueing.
lower temp??

GP100man:castmine:

[runfiverun]

hold it up to a light and see if you can see through it. check around the edges of the mold sometimes they have a ridge around there too.
if you can see light through it something is holding it open somewhere.
the pins are the next area to look.

[Le Loup Solitaire]

+1 on Bret's note....the melt is going somewhere that it shouldn't be because it is being allowed to. There is a slight warp or a high spot that is causing the blocks to not mate exactly in that nose spot. It may or may not be in the nose area, but it has to be found in order to get rid of the condition. Start with the possibility of a burr around the nose cavity, but it might be not far away in the form of a high spot. Use of a totally flat, fine stone to test and or tune the surface of each block half is a good strategy, but again the key words are flat and fine. Lino or melts that have a higher percentage of tin, will, under good valve or stream pressure cause bullets to have whiskers which can be removed with a fingernail or by rolling in a towel, but fins are another matter and the cause should be removed. Checking for light coming thru when the blocks are closed is yet another good suggestion. Some molds especially when new have to be tapped after they are closed to seat the pins at least for a while until the mold is broken in. LLS

[Nora]

I may be missing the mark here, but have you tried lubing the aligning pins? My Lee molds will do this when the pins are getting to dry.

Nora

[Down South]

jcw1970, The best advice I can give you is.
Take the mold and push out the pins.
then take a good flat stone and rub the faces
flat.
this will show if the mold is flat or warped.
This will also take off any burr you might have.:killingpc
This is good advice and what I'd recommend. I think the mould has a high spot on the lower end and a stone would find it. Try Bret's suggestion first. It may solve the problem.

[armyrat1970]

I agree with the majority, the mold is not fully closeing properly. You probably have a small burr somewhere around the alignment pins.

[Calamity Jake]

1+ for all the above, but if no fix then take a closer look at the vent lines, they may be a little deep. I have had to send back 2 RCBS molds in the last year because of deep vent lines.