I recently picked up a Danish roller with an excellent bore. It is in 11.7x56R. I tried to fit a 45/70 case and the rim is just a bit to wide to chamber. What is the best way to reduce the diameter of the rim using common household tools ? I know I can buy brass, but at $2.00 + I'd rather try it myself as I have a lot of 45/70. Thanks !

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For ammo reloaders, we generally speak in terms of fractions of an inch in decimal form, i.e., 0.005 ".  If you have a dial caliper, you might measure the diameter of the rim recess of the subject chambering, at the barrel breach, and then compare that measurement to the SAAMI specification for the 45-70 Government, which I have it to be at 0.608 ".

Do not overlook the rim thickness, since by using a 45-70 case you may be changing the "head-spacing" which is a critical component for the safety of the arm (& the shooter).  The published rim thickness for the 45-70 government is 0.065 ".

The term "just a bit" is generally acceptable for carpentry and construction work, but generally not so in this context.   

Good luck and be safe.

C.M.M.
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I've used a drill press and a file to reduce rim diameter.