I have a 40-60 Maynard.  It has the wide base brass which I have 20 cases that came with the rifle.  I need bullets to load with.  I slugged the bore but cannot find my info right now.  Is anyone loading 40-60 Maynard cartridges?  Any help appreciated.  I found my data.  This is a 1873 Maynard rifle.  I did a chamber cast of the barrel and the diameter inside the groves is right at .407in and outside it a tight .4135 to .414in. The only bullets so far is a 295 grain 41 mag bullet at .411in.

When I first got my 1873 Maynard (40-40 cal) the late Barry Darr was kind enough to make up a pair of bullet moulds to replicate the “pointed” and “cylindrical” shapes shown in the old Maynard catalogs.  I make my cases like schuetzendave, using 30-40 brass and adaptor rings made by John Bly.   
The original Maynard moulds show up on e Bay from time to time, but I don’t know of any currently produced copies.
Froggie

Just rereading this John, and noticing the bad news about the rings.  I hope you’ll be trying again since those rings are the most practical way to get usable ammo for the 1873. 

I have seen a few listings for original Maynard moulds on eBay, but I don’t know whether you’ll want to risk paying collectors’ prices for something that might be a good fit.  If Accurate or one of the other custom mould makers will make you one that it’s a proper fit.

I know it’s a lot of effort to get the initial set up to shoot these 1873s, but for me at least, it was worth it.  Special thanks to Deadeye Bly for his efforts in our behalf!

Froggie

PS  if the OP would like a small sample of the bullets from my Darr mould, I could send them to you.

Mr. Frog & Deadeye,
I have also just got hold of a nice Maynard 1873 in .40/70 thick base and would like to get it shooting again. Maynards are pretty rare out here in Oz & I've been after one for years. One original .40/70 thick head case (Berdan primer) came with the rifle but I would be interested in seeing what these washers look like on a .30/40 case. I might be able to get some of these washers made up locally. Grateful for a photo if possible. Thanks,
Spud

The Maynard M-1873 is my favorite Maynard because of the iconic rim and the ease of extraction.
Shootable ammo is readily made for a wide variety of cartridges by anyone with even a small lathe and the appropriate chambering reamer.
I drill brass rod close to the selected cartridge base diameter. Then use the chambering reamer to cut the rim with zero headspace. The final step is to part the adapter to a thickness to fit the individual rifle.
The adapter can be press fit or soldered to the case to create a nice looking cartridge but I prefer removable rings for their ease of reloading.
Attached are photos of 32-20 and 25-20 cartridges with their removable rings. The rings look best shaped in the original cartridge contours but work equally well with larger rims (25-20) or without additional shaping (32-20). 
All that's really needed is a lathe and chambering reamer for the donor cartridge.
Otto