Looking down from the top all single action revolvers, the cylinders seem to be offset to the left. On Colt and Old Model Rugers, the cylinders are well matched with the recoil shield. On the New Model Rugers, the cylinders appear to be slightly to the left even on the recoil shield because of the loading gate.
Even without a range rod you can get a good estimate of the cylinder bore to barrel bore alignment by shinning a bright light sideways into the cylinder to recoil shield gap and looking down the bore of the, hopefully, unloaded revolver.
Also, drill rods can be sort of be substituted for range rods. 11/32" for .357, 13/32 (or better a "Z") for .44, and a 7/16" for .45.
You have to check ever cylinder hole.
The problem often is caused by a poorly fit cylinder latch. I have an Old Model .357 with this problem. I solved it by shimming the cylinder latch bolt, making the shim from a feeler gauge.
A cylinder which is sitting a bit low can be raised by installing one of Kyle's Belt Mountain cylinder base pins.
John