As Bob noted above, this is the bench position I use when shooting my rifles - all of them that have any recoil that is.

If you sight in a bolt rifle, like a 9.3 or .375 or even the kickers in muzzleloading rifles such as a heavily loaded .58 and .69, by letting the forend bounce on the front rest, then shoot it hand held as when hunting, you will usually see a marked difference in point of impact. This is over an above any regulation of 2 barrels. It is little wonder why some people have a nasty time of it. The same hold no matter what, is vitally important in normal rifles, let alone a double rifle that was originally sighted by holding.

The difference can be enough to miss at extended ranges, or worse, make a poor, wounding shot. This difference recoil induces point of impact can cause poor, wounding shots on game or outright misses, as close as 100yards in scoped bolt guns & completely destroy the regulation of the sights in a DR.

Rifles that have 'some' recoil, will change impact depending on how you hold and shoot them. The rifle must be held as if you are shooting offhand - rest the back of your left hand (right handed) or right hand (left handed) on the bag, but grip the stock or barrels as if shooting offhand and sit so the gun can recoil, just as Bob indicated.

The differing point of impact depending on how you hold, is another reason why 2 people sometimes cannot shoot to the same place with the same rifle.

Case in point on holding is my 9 pound .375/06IMP. If I shoot it letting it bounce on the front bag, held as a bench rest rifle as I see many do and sight it in, the point of impact is 3 1/2" off the rifle's zero - at 2 o'clock. 3 1/2" doesn't sound too bad, but that's off a rest - add in a bit of wobble for offhand and it could be 6" or more, and a high miss or 'graze' on a target as large as a moose or elk.

However, if I shoot it hand held as I sighted it in, it does not change point of impact whether I'm shooting offhand, off the bench or sitting or even resting against a tree. As long as the stock is held n my hands, it hits where it's pointed & I can trust the sights.

I always wear a PAST shoulder pad when shooting the kickers, now - due to some old shoulder injuries. With the standard Magnum PAST pad, I can shoot just about anything - but without the pad, the heaviest kicker I can shoot is my 9.3x57 and only for a few rounds at that, like when hunting. That is probably why it's my new favourite.