I reloaded for a Type 99 7.7mm in the 80s. By the books correct cases are supposed to have a little bigger head dia. than .30-06. The head diameters of Norma 7.7 cases measured the same as .30-06s and so were a waste of money. You can easily shorten .30-06 cases in a variety of ways. I found it fastest to 1st cut them with a small tubing cutter then flare the new pinched in "case mouth", FL resize, then put them in a hand cranked case trimmer. The resulting case head to chamber fit was no worse than a lot of M1 Garrands.
My old 7.7 appeared at the range in the hands of a shooter who had paid $25 for it and $10 for an old Herters die set. It passed through 3 or 4 shooters at that range along with the dies at $35 before I sold it at a gun show. Every owner got 100 yd. 5 shot groups in the 1 to 1 1/5" range off sand bags before loosing interest in it.
Best Regards,
Gil