Need advice on custom .401 mold

[rufracer]

Im thinking of having a mold made for very heavy .401 boolits. Somthing like the
Lyman #410660 40 Caliber (406-410 Diameter) 385 Grain Semi-Pointed but in .401. For my 10mm mag

my options are to either have the mold made in .401 (bore riding) or order a custom reamer that would acomidate the lyman sized down to .401-.402. My bore is .392 and my groove is .400. Im guessing the bore ride dia. on the lyman is about
.400-.403 so Ide have to have one hell of a leed, therefore Im leaning toward the custom mold.

Am I right in saying I want my dore ride dia. to be .393 on my custom mold?

[Piedmont]

rufracr, Tell me about your cartridge. What is it based on? How long is the neck? What speeds are you seeking? BP or smokeless? Gas check or plainbase? What kind of action? What bullet hardness will you use (it can make a difference on bore ride size)?

I would go custom on the mould but the hardness will matter on the size you might want for the bore ride dimension. If it is very hard you don't want it very much over bore dimension or it just won't chamber. A softer bullet can just engrave and still chamber.

[rufracer]

its going to be a 10mm mag in a ar-15, with a long oal. Ill be running mostly sub-sonic 950-1050fps.

case length is 1.245-1.255 with about .8" of "neck"

[Piedmont]

rufracer, That must be some kind of a bottleneck. Make your band section around the length of your neck. I don't think you can get gas checks in .40. If that is so you will want your bullets real hard (in my opinion). That means you don't want your bore ride to be over bore size and the semiauto action leads us that way too. You don't want jams when the bore ride wedges into the rifling.

Basically then your band length is limited by your base of the neck to throat length. Your nose length is limited by your magazine. I would probably tell the mould maker I wanted a .392 nose. The big question is will he be able to hold to that. I think on Mountain molds website he specifies requested diameter to .002"+. If he makes it .002 larger on the nose you are sunk.

I'm hoping some others will chime in on your project. It sounds interesting.

[rufracer]

I was mostly wondering about the bore ride section. I can fix the reamer design to acomidate whatever bullet I want, if I have to. I should have about 1" extra magazine length. The case isnt botle necked. It is just a 10mm auto stretched out about 1/4" it just bulges if you seat the bullet too deep.

I think I will ream to use .409 boolits sized down to .401 so mold are easy to find, unless someone has a better idea. Thanks for the good info.