Can any knowledgeable gunsmithing types help with this query: I have a Ruger # 1 in .458 Win Mag which I want to ream to .458 Lott, can the same reamer also be used to ream out .458 Win Mag full length loading die to .458 Lott so I can full length resize Lott cases?

The answer is NO!!!
They are slightly different reamers.

Buy a new die from RCBS, Rsdding, or whoever you like.

unless you are running top loads, you can easily load lott with 458 winnie...

it you are dead set on recutting the winnie dies you'll need a lathe, a torch, the proper reloading reamer (it's not the same as a finish reamer) and some hydrolic oil...

heat the winnie dies to a bright cheery...
hold for 5 mins....

let cool (air cool) do not quech!!!

when cool to the touch, spin it in the lathe... running the reamer in...

polish
after polishing it,

take back to a dull cherry....

pitch into the oil....

polish...

no reason to draw it as you would lke it to stay hard

or, just buy some hornady dies from midwayusa

jeffe

Think about it a minute. The chamber reamer die has to cut a chamber that is slightly bigger than the ammo. The reloading die has to squeeze down the brass to slightly less than chamber dimensions. If they were the same dimensions then you would have a hard time putting ammo into the chamber. As you can see from what Jeffeso described you can ream out your reloading dies, but you have to have a special reamer made and that would run you around $150 or so from most reamer makers. A new set of dies is a lot cheaper. You can also sell your 458 Win dies if you will no longer be loading 458 Win Mag. Your question was a good one and one that I have heard often.

I wonder if spacing the die bottom off of the shellholder, using a spacer of a thickness equal to the case length differences would work for sizing? Surely backing off the seater die should work?

I believe the Lott is just a little longer than the Win Mag; not positive. Just a thought; not sure if it will work, but might be worth a try. Safe and Happy Shooting! Joe

Don't be cheap it always works out dearer in the end

There not great but Hornady .458 lott dies are around $25US from Grafs and Sons, the ammo they make goes bang and they shoot alright.