Key is too find which mftr made the reamer and if the reamer owner has the reamer print number. You can go to the mftr (PTG, Manson, Heirickson, Clymer etc) and order the same reamer cut to the same specs.
You can use a COW type fireforming or use a false shoulder method. I personally like the false shoulder method. It forms first time to the chamber where as the COW might not. www.6mmbr.com
has an article with pics showing how to do it.
Basically if you have a 30-338, use a neck bushing die to partial NS the brass to where it it just close with a slight tightness in the chamber. test one case to determine amount of powder needed to fully form the case and then do the rest. You will have to shoot all cases, but you normally have to do the same thing at least once with the COW cases.
Most of the standard die mftrs are 3-6+ months on dies and $200. For that I would go with the Neil Jones dies from www.neiljonescustomproducts.com
. IMO these are the gold standard dies from anywhere. My delivery time was about 40 days or so and $366 with three shoulder bump bushings. and micro seater.
Tom Sarver in Ohio has a shortened 30-338 called the Hulk that holds the 1K light gun records of 1.4xx, perfect 50 score and 5Xs. The cases had 54 loadings on them when he shot the record and he retired the cases at 80 plus reloadings. He shoots both the 240s and 210s. JLK has a new 210 with a .680 BC also.