Some time ago I picked up a barrel marked 6mm/30-30 and forend from a member here who had shot it on his 44 1/2. It was very nice and uniquely made mostly round barrel with a 3 of the 4 sides at the breech square and grooved for handmade scope mounts that were included. I realized, that as is true with modern CPA 44 1/2s, it would have to be reworked in some fashion to fit my 44 1/2 and my smith accomplished this by chasing the threads and such and only losing .015 inch of the chamber. He reset the rim recess to restore headspace and all was well on that end. Now I needed brass. It turned out to not be difficult to make. I took new 30-30 brass with a normal lube pass and full length sized it in 30-30 dies to establish minimum dimensions and perfectly round the necks. Next, I finger wiped the neck and ran it full length into a 270 Baby Titus die (don't ask, I have no idea where it came from) followed by finger wiping the neck again and full length sizing in a 250 Savage die. The next step involved a 243/244 Lee Collet neck sizer that I had shortened by grinding to a 30-30 length. By the way, this die is made such that any angle/width of shoulder in the final case would be no problem. I made a holder that allowed my Harbor Freight mini chop saw to cut the neck off to just a couple of thousandths over my desired length of 1.905 inches which was attained by a quick pass through a Redding case trimmer. At this point I had no real handle on what the shoulder was going to look like once fire formed  (the failed chamber cast was another story) but only that the case was an appropriate length and would chamber easily. I had some .244 gas checked bullets and 8.5 grains of Unique made a nice fire forming load. Finally an anneal of the new neck/shoulder was done and the brass was ready for load testing. Voila!

Here's the complete transformation: L to R - sized 30-30; 30-30 necked for .277; 30-30 necked for .257; 30-30 necked for 6mm and ready to trim, load, and fire form; 6mm/30-30 trimmed, fire formed with 85 grain lead bullet and 9 grains of Unique, and annealed.