Lapping Lee sizer die using 200-400 grit in boolit GG

[Hang Fire]

I have couple Lee sizer dies that need opened up larger. Thinking of putting some valve lapping compound in the GG of some boolits and see how much effect it has.

[saz]

I have opened up a few of them, and what worked out very well for me is this:
I took a brass cleaning rod, wrapped it in 600 grit emery paper for a tight fit inside the sizer.
Chuck the rod in a drill, lube with lots of WD-40 and start turning slow moving the rod in and out of the sizing die. (non-directional finish and keeps the hole round)
Just go slow and check the size often. I usually stop .0005" short of my goal and switch to a lighter grit to "polish" up the inside a bit which takes up the remaining .0005". Works like a charm!

[MBTcustom]

I agree with saz. You want to use a lot of sandpaper and keep it moving. Sandpaper looses 90% of its cutting ability very quickly, so if you just keep using the same worn out piece, you will be spinning your wheels.

[geargnasher]

Using a boolit and paste abrasive is likely to dig grooves in the die. Sandpaper is better. There have been some good threads on how to open up a die with a drill and sandpaper.

Gear

[youngda9]

Dowel rod wrapped in sandpaper. Put the die over the rod and paper. Hold both ends of the rod and roll back and forth on your leg. The die spins and it gets opened up symmetrically. Wear some old blue jeans.

[Shiloh]

200 is probably overkill, and I wouldn't use it for long. The two that I did were done with #400, then #600. Then I went with 1200 or 1500, and buffed with FLITZ.
My boolits are sized to .3585 and look like little mirrors.

Shiloh

[Hang Fire]

I have a lathe and easily opened up lube/sizer dies using using abrasive cloth &c.

I wanted to try it as decribed in OP, to find out just how effective and labor intensive the process would be and was curious if others had tried it.

Using abrasives for lead lapping bores by hand and fire lapping is a common practice which produces very good results, so will see how this goes.

[Iron Mike Golf]

I don't know how hard the steel is in a Lee sizer die, but a SAECO is real hard. Trying to use a boolit and 320 grit lapping compound was pitifully slow.

I used a pin gauge and emery cloth, then used 320 and 600 grit lapping compound with boolits to polish. Finished with Flitz and a felt polishing pad.