7mm International Rimmed

The 7mm International Rimmed is a wildcat cartridge developed by Elgin Gates in the seventies. Nothing strange about it, take a 30-30 case, neck it down to 7mm, and there you are. You don’t need to trim the brass or anything.

Before (bottom) and after fireforming.

Compare this to the 7-30 Waters, developed by Ken Waters (also in the seventies) specifically for levergun use. It’s also a 30-30 case necked down to 7mm, but in this case the neck is much shorter, giving more case capacity and of course more velocity.

30-30, necked to 7mm, and fireformed. (Image source: levergunscommunity.com)

I’ve been shooting the 7mm TC/U in my 14″ Thompson Contender for a few years. Nothing wrong with the cartridge, shoots great, adequate power and everything… but the 7mm TC/U headspaces on the shoulder, and that means that if you don’t get your resize operation just right, you either can’t close the gun, or your brass stretches and the case head separates after a few shots. I carry a tap in my shooting box, this has saved the day for me and for at least one other shooter caught with half a case stuck in the chamber. A TC ideally needs a rimmed case.

So I had the choice of 7-30 Waters or the much less popular 7mm IntR, and I chose the latter because, as I said, the 7mm TC/U already has enough power for what I need to do, I don’t need power, I just need a rim on the case.

7TC/U : 25.5gr S335 : 145 grain cast RCBS-145-SIL : 2000fps : my 7mm TC/U silhouette load, accurate.

7mm IntR : 29gr S335 : 160gr jacketed : 1900fps : accurate, 3 shot velocity spread = 6 fps, SD = 3.

7-30 Waters : Factory load : 120gr Nostler : 2400 fps from 14″ TC barrel.

I think 7mm International Rimmed is the best 7mm TC silhouette shooting option, now to do some further load development.