Is it the fit of the mold?

[Woodchuck]

I just started to use my Lee dies the other day and they leave little "fins" (for lack of the proper term) on the sides where the 2 halves meet. I've tried everything I can think of to make sure they are clean and tight. Is there a cure for this or do I need to run them through a Lee sizer to clean them because a knife takes forever.
I have the TL 148 .357 and the TL 175 .401.

[Pat I.]

Hold the blocks up to a strong light look in the cavity and see if you can see light were they meet. If you can something's holding them open.

[montana_charlie]

What kind of 'dies' are you talking about?
If you actually mean a 'bullet mould' is leaving fins on your bullets, the mould is not fully closed...or your alloy is way too hot.
CM

[454PB]

What usually causes this with Lee moulds is that they are not aligning properly when you close them. Lee tells you to lubricate the alignment pins (horizontal alignment) and block "V's" (vertical alignment) to keep them properly engaging. I quit doing this many years ago, I now close the blocks while watching their alignment and adjusting if needed by placing the sprue knocker against the bottom of the block halves.

No matter how careful you are with lubing the mould blocks, eventually that lube migrates into the cavities and pollutes the boolit.

[DLCTEX]

I've had no problems with lube migrating since switching to Bullplate lube and applying it with an almost dry Q-tip while the mold is hot. It's amazing how little it takes to do the job. If there is lead sticking to the mold faces I dip the mold in the melt to heat it and then wipe with 0000 steel wool. DALE

[buck1]

The blocks could be warped? Buck

[Echo]

I had the problem with a Lee mold - turned out to be a small burr on one of the alignment grooves. Took that off and lubed (lightly) the aligners again, and started casting good boolits.
Check it out...

[HeavyMetal]

My experience with the Lee 2 bangers is the same as 454pb's!

I use my leather gloved hand to make sure the mold halves close properly, watch the top of the mold when closing for a flat fit where the sprue plate slides.

Remember the bottom of the molds are never square or flat so don't depend on that as a closer system.

I quite lubing as well but I have tried, and do like, the bull plate lube used very sparingly on the pins and v blocks ov the 2 banger Lee's.

[Woodchuck]

I tried lightly filing the mould faces to remove any burrs but I haven't lubed them any.

[montana_charlie]

I tried lightly filing the mould faces to remove any burrs but I haven't lubed them any.
Did you file at the corners...or across the flat faces?
CM

[Woodchuck]

Across the flat faces.