I realize I'm probably the only one here that gives a damn about breech seating. But here goes anyway.
Breech seating requires that you bring loaded cases to the range along with separate bullets. Cases are easy. Just use an ammo box. But bullets can be a challenge. When you add a competitive match to the mix, it could mean mutiple boxes of stuff on the bench along with the other stuff you normally have for a match (spotting sheets, score sheets, sight settings, breech seater, etc.).
So, today I started thinking about a solution and decided one ammo box to carry both bullets and charged cases was the way to go. I thought I might be able to squeeze 60 cases and 60 bullets into a 100 round MTM plastic ammo box. Caliber is .38-55 in my case. But you might be able to get this to work for .45-70 if you are so inclined. Smaller calibers like .32-40 or .30-30 would be a snap.
I took the inside dimensions of that MTM ammo box with the 100 round insert removed. Made a drawing to establish the centerlines for 60 cases and 60 bullets to fit in that envelop. Went back into the shop to compare the dwg. to the box and realized it might be much simpler than I had envisioned. I had planned to make a new insert for the box. But that was not necessary.
I ended up making an insert/adapter that fit on top of the existing cartridge insert. I needed the back 6 rows for 60 cases. That left the front 4 rows for bullets. I measured the room that was left and then compared it to the bullet portion of the drawing I made. The sizes were identical. So, all I needed to do was make the bullet insert from a piece of 3/4" pine. I have a bunch of primed pine lumber left over from a coffered ceiling I put in the master bedroom. This stuff is finger jointed lumber that comes primed to hide the joints. The good thing is it is dead straight and dead stable. And when you drill it, it does not tear apart like some softwoods. Here is the final product.
Before showing you the other sides of the insert, here is a view of the box with the OEM 100 round insert. Note the small ribs on the sides that locate the insert in the box. We will use these to secure the bullet insert.
This is the bottom of the insert. Note the 6 slots cut on the front face and the two side to engage the ribs in the box.
Here is one of the side of the insert. Note the 5 deg angle cut into the forward end. This is required to mate up to the wall of the box, which is made at 5 deg. You can also see the slot for the positioning rib.
Here is a view looking at the front edge. Again, you can see the two slots for the positioning ribs in the box and note the 5 deg angle cut into each end. Lastly, there is a radius to the inside corners of the box. So, for a nice tight fit, you need to radius that front end to mate up with the inside of the box.
The ribs keep the insert from sliding in the box. Plus they also "grip" the insert to keep it from falling out. I can turn the box upside down and the insert stays put.
Oh, and pay no attention to those undercuts made along the bottom of the insert. I had not pushed the OEM insert back in all the way and when I first started to fit the insert to the box, I thought I needed to provide relieve for a small shoulder. But when I realized that the insert was not home, I pushed it in, and that little shoulder became the actuall sides of the box that the insert mated against. Only you and I know that cut is there. Nobody will see it with the insert in place. It will be our little secret.
Now that I look at it, I think I'm going to have to paint that insert back to match the OEM insert. It's already primed, after all.