October 2011
There's very little information on this cartridge available on the web, so...
The Reload Bench has a copy of the entry from Cartridges of the World, as does The Reloader's Nest. The Handloader's Bench is a slightly better resource, with a post by Rapier giving a number of loads, and a further post stating that the brass should be 2.040" long.
The most definitive resource I've found is The Gun Digest Book of Metallic Silhouette Shooting by Elgin Gates.
Elgin Gates designed the IHMSA range of cartridges in 1975 or thereabouts. These included .25, 6.5mm, .270, 7mm, .30, 8mm, .338 and .35 calibers and were based on the .308 Winchester (or .30-06, or 7x57, they're all basically the same case) brass. He then also developed the International Rimmed range, using 30-30 brass and later .375 Winchester brass cut down to size (.375 Winchester brass is stronger than .30-30 brass). For various complicated reasons, the rimmed range works better in guns like the T/C.
Gates kept the 2.040" length of the 30-30 case, i.e. no trimming of the brass is required. In single-shot handguns one doesn't typically crimp the bullet, and the long neck of the 7mm Int R gives lots of neck tension, so exact brass length is unimportant -- mine mikes to about 2.050".
Gates gives loads for typical American powders, pushing a 154gr bullet to almost 2200 fps out of a 14" T/C barrel.
I tried S335, since it's close to H322. Gates notes that 30 grains of H322 is "hot" and I tend to believe him (in the seventies, silhouetters really pushed velocity, they were not afraid), so I started at 24 grains and worked up to 30 slowly.
29 grains of S335 showed promise, with a 35mm 3 shot group at 50m, but the next time I tried it results were not as good, so maybe it was a fluke (three shots are not really enough to judge).
29.5 grains of S341 (which is similar to IMR4895, BL-C(2) or W478) gave me a 39mm 5 shot group at 50m.
For all of my experiments, bullets were some 160 grain Highland I picked up at Kings last time I was in Durban, probably seven years ago. And since I havn't mentioned it, this is for my 14" T/C barrel from MGM, 9" twist, gorgeously chambered by Mike Bellm.
since 2011-10-11.