So slugged my new Shiloh Sharps 40-65 barrel and got a groove measurement of .405. I picked up a SEACO 740 mold and on its initial casting it’s dropping .411 bullets. In most articles I’ve read they’re recommending.001 to .002 over groove. How far would you recommend sizing these bullets?

Thanks Skeeter

Are you sure it is .405"?
My Shiloh Sharps is the standard .408 and I shoot .410" diameter bullets in it.
The measurements between land cuts on a bullet are difficult to measure accurately.

I was using calipers to measure but will also need to check with a micrometer. If it’s truly.405 I’m thinking ordering a BACO money in .408 that could be resized down to .407 or .406 or left unsized. Will probably need smaller neck expanders too.

Just talked to Shiloh and Lucinda said all their 40 cal rifles should be .408. Will need to reslug and measure again or just assume it’s good and reload as it’s a .408.

Bullets can be sized down quite a bit more than most folks think and still be quite accurate.  The trick is to do it in steps of about .002" at a time and do it nose first not base first.
I like to lube them in the first step without sizing or only size down about .001" when lubing.  You can get any diameter nose first sizers from Lee Precision  You can also us a lube sizer press for nose first sizing if sizing only. 
There are a couple ways to do that.  you can remove the ejector pin from the sizer die and just push the bullets straight through and catch them from underneath.
You can also do it by leaving the ejector pin in the die but screw the depth adjuster all the way down and at the same time adjust the push plate on the bottom of the guide rods so that on the up stroke it pushes the bullet out just far enough to be able to grasp the bullet with your fingers. This leaved the ejector pin far enough in the die that it aligns the bullet when dropped in nose first. I use a flat nose punch for this.  This is with the RCBS lube-a-matic. With the Lyman lube sizer you do not have the ability to adjust the return depth of the ejector pin so when doing this with a Lyman press you have to manually control the ejector depth by only raising the op handle part way up.  Done in this manner .010 to .012" is not unreasonable.  I regularly size 45 caliber rifle bullets of anywhere between .458" to .461" down to .450" for use in 45 caliber muzzle loading rifles and accuracy is as good as bullets that are only sized to the accepted norm of about .002"