Just like a magnum rifle you will have to hold just a tad tighter to get consistent groups from a lot of magnum revolvers. You can hold a 22lr pretty loose and get a decent group(not promoting this as accuracy what so ever). On a lot of magnums you actually have to really concentrate on holding the gun in position as it goes off. Shoot it loose and all most all of them will be inaccurate. It don't have to be a magnum to shoot poorly if your not holding the gun on the target the whole time before the bullet leaves the barrel. Try a flintlock pistol and that will more than prove what I'm saying.

Here's how I shoot a pistol or revolver to help eliminate extra movement while shooting. My grip consists of mainly the last two fingers on the grip. The third finger and the pinky finger. You can use those two fingers to grip it real tight and not cause it to shake or and to pull left or right depending on which hand you use. The middle finger doesn't have much pressure on the grip and of course relaxes your trigger finger in the process. It makes a L shape pressure on your grip being your saddle between the first finger and thumb also applies pressure on the grip. For me it really brings a lot of control to left and right issues and muzzle jump. The supporting hand is mainly your stabilizer. I maybe totally full of crap on this but it sure has enhanced my shooting with handguns.