Depending on the weight of gun and length of the barrel it varies from holding rear bag with left hand to holding forearm down or even downward pressure on the scope (don’t want to influence barrel) for an ultra light short barrel that has to be tamed. Otherwise they’re super hoppy. The light hoppy ones seem to do some weird inconstant things if I don’t tame them, especially when shooting off a bipod on concrete.
For the vast majority of us mortals, shooting sticks are a complete necessity when shooting offhand over anything but short distances I was hunting muleis in Utah and we spotted a walking mulie about 450 yards. He disappeared while I tried to find a rest. He seemed astonished I couldn't shoot that far offhand. Clearly God did not make us to have equal shooting skills. I had never met anyone who claimed to be able to do that.
Off hand, standing, kneeling, off sand bags, tripod, in a shooting rest/vise, ect. I all ways hold the forearm. It's how I was taught at a young age and it works for me. As stated many times in previous post find what works and stick with it.
I have 2x300 Win Mag rifles amongst my selection of nearly 20. One is a Merkel Helix Aplinist which I use to shoot driven wild boar and mainly shoot it standing like a shotgun. I do also use it for lightweight hill stalking where I shoot it either off sticks or over a pack. My Remington 700 XCR is used either for target or longer range hunting and this is either on a bipod, off sticks or rested on my pack.
Both rifles when rested either on packs or bipods are 1/3 MOA and I can achieve this either holding the fore end or in a variety of positions as determined by conditions.
What I do find is that practice is the key. If you only practice one hold, you can only shoot one hold reliably which does limit you when hunting or target shooting in less than ideal conditions. If you practise it you will find your way.
I hold the forearm on all my hunting weight rifles. On my heavy target rifles i dont. Like many have said it's a weight, recoil pulse and repeatability. I do initially dial the rifles in with a champion gorilla bag so I know what the gun is capable of.
I have been shooting for nearly 55yrs now and have shot anything from a 22 rim fire through 50BMG, Mortars and a variety of 1980s anti tank toys.
Today things are a little more pedestrian.
For hunting I mainly use my 2x300 Win Mag rifles. One is a Merkel Helix Alpinist the other a Remington 700 XCR, quite different rifles used in different ways.
The Merkel is mainly shot off hand shot like a shotgun with a 1-6 scope at ranges up to 150yds, mostly on driven boar, the Remington mainly for longer range deer, up to around 300-350yds, off a bipod, sticks, high seat rail or pack. I don’t normally dial whilst hunting I just hold for condition/wind/longer ranges.
The Merkel is set up with an MPBR of around 270 yds using either 180gr pr 200gr Partitions or the 220gr Sierra Round Nose. In the Remington I use either 208gr A-Max, 212gr ELDX, 180gr or 200gr Partitions or A-Frames but both rifles are ALWAYS shot with my left hand holding the forearm, just like a shotgun, if I’m using sticks I hold the for-end into the notch to help see impact point, on a bipod with a little downward weight for the same reason, on a high seat rail, pack or other improvised rest, between the for-end and rail/pack etc to isolate the for-end from the rest material for consistency.
Having said that, I also shoot F-TR (308 Win) out to 1000yds to a fairly high standard (Gold and Bronze at the European championships) and shoot off a SEB bipod and heavy rear bag and my hand NEVER holds the fore end it’s either at the SEB adjustment arm or on the ears of my rear bag.
There is one thing that I do with ALL of my rifles though, I practice, and I practice a lot, most weeks sees me at the range at least twice, nothing beats repetition, there’s an old saying, beware the man who has only one rifle and shoots often, chances are he will be good.
Many of the guys I shoot with in F-Class have very different gear and techniques to my own but the good ones, like me, practice, a lot, so my recommendation would be find what works for you, be consistent in what you do, develop an accurate load in an accurate rifle and practice lots, take good counsel from someone who shoots like you but is better than you, enter competitions to hone your craft and skills, you will find your peak but along the way you will have a good deal of fun and make new friends.