I was a US Army sniper for a handful of years, and last month I bought a new Christensen arms ridgeline FFT in 300wsm. I would have been willing to bet large sums of money that I could accurately shoot any rifle placed in front of me, but I was proven wrong. I was shooting this rifle really poorly, like 3moa. I tried a couple different types of ammo and had similar results. Before filing a warranty claim I took it out of its 1.1lb carbon fiber stock and put it into a mini chasis and it shoots .75moa with factory ammo. I had to begrudgingly admit that I was the problem. Decades of shooting 10lb-15lb rifles with vertical grips had ruined me on shooting a sporter type stock well. So, I sold that stock, bought a used xlr envy, and now it's a 10lb rifle with a vertical grip that shoots very well. My buddy 338dude witnessed this series of events. I guess that's why I jumped straight to that idea, because it is so fresh on my mind.
Not to argue, I fully admit I struggle with light magnums, and I think most of us would be better served in the hunting world of shooting for that 10lb rifle for big magnums not a 5.5lb rifle, but it also could be the stock/action interface, I think the FFT is pilar bedded so probably less likely in this case. I've seen tons of light factory hunting stocks where the action was moving in the stock, even with bedding blocks, especially with big calibers, others where the stock had rub spots on it from contact with the barrel. The point is well taken though, it's hard to get these ultralight magnums to shoot well and more often than not the shooter is part of the issue.
This is one reason I really dislike the practice of manufacturers accuracy testing barreled actions outside of the stock in a machine instead of shooting the barreled action in the stock. It removes something we know to be a significant component in rifle accuracy. The stock/action interface. From a manufacturers standpoint I get it, it's faster and more consistent than having a human shoot the proof groups, but if the stock/action interface is an issue, you just end up sending a bad gun back to an already frustrated customer.
One thing I think that you hear talked about a lot in other shooting sports, but not in rifle shooting is the mental side of things. I used to shoot on a national level in Trap, and dove quite far into archery, and lot of the same mental aspects of those sports apply to all shooting disciplines but you read almost nothing about the mental side of a shot routine and practice for rifle. Some of the small bore guys have written a lot.
For example, you can flinch because of recoil, or you can flinch because of "panic". In archery we call this "drive by" shooting, it's where your brain desperately wants the sight to sit still but it won't, and the more movement the more your brain panics and the more you "punch" the trigger when you think the sight picture is right. It's why many archers struggle if they change to shooting a powered scope lens. I'd imagine this could easily happen in rifle positional shooting where you will never get a rock solid position. I also would not be surprised if more than a few shooters have this same issue shooting 30+ power rifle scopes now. The same is true for aiming, it's a mental art form. You will see archers that struggle to shoot well on a large round bullseye target, but shoot very well just shooting 1" orange sticky dots. It's because their brain is not focusing hard on their aiming spot with the larger round target, with the tiny dot it's easier to focus (it's the old "aim small miss small" thing. I've seen the same with guys shooting big steel targets, if you put a little sticky dot on them their groups will tighten up, as they have a small focusing point for aiming. I also believe pressure to shoot tiny groups can be counterproductive to shooting at 100 yds and is why some shooters do better shooting a longer ranges, it's more "fun" and they don't stack as much pressure on themselves. We all expect to shoot 1/2" groups at 100 yds, but if you set out clay pigeons at 500 yards, that's just fun, and most of us don't expect to hit them all, so the brain can relax a bit and just execute.