I actually read every post in this thread, which apparently some have not. (But that's usual on the Campfire. Most folks just read the OP and then respond, even if 100 posts have already thrashed over the same stuff.)
The people who have never experimented much with shorter barrels have trotted out all the old BS: that 250 fps will be lost, that the rifle will turn into a 7x57, that you'll have to use a "faster" powder to make up for the shorter barrel, etc.
None of this is true. A larger rifle cartridge ALWAYS will get more velocity than a smaller one, in any legal-length barrel. The velocity gain will also follow the same 1/4 rule, no matter the barrel length: Velocity gain will be at 1/4 the rate of powder space gain.
Also, the same powders that get the most velocity in longer barrels will get the most velocity in shorter barrels. In a 7mm RM the fastest powders will be the usual suspects: IMR7828, H4831 and H1000, RL-22 and RL-25, Ramshot Magnum, etc.
There is no way to determine how much velocity loss will be without shooting, as different loads will lose different amounts. I have seen the same barrel lose anywhere from 15 to 60 fps per inch when shortened 5 inches. The burning rate of the powder didn't matter; some faster powders lost more than some slower powders.
One general rule, however, is that the LEAST amount of velocity loss in shorter barrels is with heavier bullets and slower powders. This is counter-intuitive, and contrary to popular myth, but I have seen it over and over again in various rifles.
There have been experiments run on shorter barrels with decibel-measurement equipment and no, they are not a hell of a lot louder. What really up the decibel level is a muzzle brake or a much larger bore.--but as some perceptive person already noted on this thread, ALL big game rifles are loud. They will all make us deaf if we don't use hearing protection.
Once again the people who have actually shot shorter-barreled magnum rifles have posted good information, and those who never have posted the same old general misinformation.
I've owned several 22" barreled magnum rifles and there isn't enough difference in the ballistics to ever notice in the field--and they have all still produced "magnum" ballistics.
