So this is a new loading venture. I have a Meecham that I inherited. I have about 250 rounds of brass. I do need a mold and not sure what to get. 
I also am not sure I have the correct brass. Will I need to make a chamber cast? Or did Meecham use a certain version? 
So any recommendations on a bullet mold and how to know what brass is correct( this is buffalo arms made from 30/40 Krag)
Jeff

I would do a chamber cast, to be sure and get the throat and first inch or so of the rifling, so you can get a good measurement. Then do as Arnie says and check the rifling twist.
Don't be surprised if the groove diameter turns out to be .403 and the bore somewhere around .398ish, with a 1-20 twist.
nForm there it's just a matter of selecting the right length of bullet, probably something around 1.1 inches long, and keeping a good supply of 11/2 or 1 f powder on hand and figuring on using around 65-70 grains depending on what the target tells you.
The 40-70 can be a picky bugger but once you get thru arguing with the thing and listen to what it's trying to tell you they will shoot quite well.

So here are the measurements so far. I take them with a grain of sand as this is my first go around. So I appreciate a little patience. 
I started with a bullet sized .412 and pushed it through the bore sarting at the breech. I measure .400 and .408 with ROT at 1:16. 
I used dial caliper and micrometer. 
Jeff

That sounds spot on for today's modern barrels. Since it's a Meacham he was probably using something like a Badger barrel. If you inherited the rifle and it came with Buffalo Arms stretched brass, you should be good to go unless there's something out of the ordinary going on. Get a good bullet mold that casts about .409" or .410" and weighs ways around 400 to 410 grains. I shoot a bullet a little longer than the one Arnie recommends and I don't see any tipping on the target until past 800 yd. Get some one and a half Swiss powder and start with about 67 to 69 grains and compress it very lightly with a compression die. You will have to experiment with this to get the right amount of powder and bullet seating depth as each rifle is different from another. Add a .030 fiber wad and set the bullet on top but don't use the bullet to compress the powder. Seat the bullet just gently into the lands or slightly off and you should be seeing some pretty fair accuracy right from the beginning. Let us know how it goes. My first black powder cartridge rifle was a 40-70 sharp straight and I shot it for several years and did quite well with it in Long Range matches.

A chamber cast is easy to do and is really important.  The bullet that you shoot should match the diameter of the freebore right in front of the case.  It is also helpful to know how long the freebore is in case you want to go with the paper patched bullets.  A dual diameter paper patched bullet makes a great traditional hunting bullet.  I cheat with my 40-70 rifles and use smokeless for the hunting loads with a dual diameter 330 grain bullet.  I have 2 rifles and they both use different brass.  Use a depth gauge to measure the recess for the rim in the chamber to see what thickness of rim you need but if you got brass with the rifle then you most likely have the right brass.  The one thing about BPCR that is different in reloading is you really don't need to resize the brass if you pick out a bullet that is a finger slip fit into a fired case.  That bullet should be close to the freebore diameter as well.  I use a nose diameter that is .002 below the bore diameter to allow to chamber with a fouled barrel.  Accurate Moulds has dozens of 40 caliber moulds and Tom allows you to tweek the dimensions to fit your rifle.  I would not go any heavier than a 370 grain bullet unless it is for long range target work.  Don't be afraid to try paper patching either.  Arnie (Beltfed) can show you pictures of groups fired with dual diameter patched bullets that will certainly impress you.  Have fun learning!  I started shooting 40-70 about the time Covid hit so was able to spend lots of time learning how to cast a good bullet, how to lube and also how to patch.  Tom