I have a .45-70 that is short chambered by a solid 1/8" with no throat. I discovered this first by shooting it and getting keyholed bullets. Then I did a chamber cast and actually can see the problem. What kind of reamer do I need to fix this problem?

How in the world did you get a 45-70 to chamber in a chamber that short in a springfield?

If it is the full chamber that is short you need a finish chamber reamer. If it is just the throat then a throat reamer. Guess you could also cut only the throat with the chamber reamer. If you can't borrow several places rent them.

It was a tight fit there is no doubt. How can a chamber be cut short but still have the groove for the case rim in place? The chamber dimensions are correct, it's like the reamer did not get cut in deep enough. I have heard of finish reamers before, is that a possibility?

A finish reamer is just as the word implies. It's for finishing the chamber after you have roughed it either with a lathe or roughing reamer. I wonder if your chamber was cut with a chamber reamer that didn't have the throat portion on it. There are reamers that just cut the chamber, then you use a throating reamer. Other reamers are complete and cut the chamber and throat both. If you get a finish reamer that has the throat too, make sure you use the right size pilot on it because that centers it. Too small a pilot and you may cut your chamber off center. Why don't you just have a gunsmith examine your rifle and see for sure what you have going on?

here is a link to a jpg of the cast and cartridge

http://s1080.photobucket.com/albums/j333/bigotto1/