This is such a great forum, there are some really good posts here. I think it's an important topic too.
Many of us grew up shooting .22's, and after a few boxes of shells it ain't no thing to hit a spent 12ga shell at 25yrd. So why is shooting CF off hand so hard?
I think
@WildRose post #5 and
@Lonewolf74 post #10 are onto something.
For years I practiced exclusively offhand. I tried a lot of different techniques. Some worked, some didn't, and others just didn't work in the field.
In my experience, being able to 'hold' small requires a high degree of fitness, and a 'silhouette style' position (feet almost perpendicular to the target, support hand under floor plate, elbow on hip). Though cardio fitness is a real asset, I've not found the 'target style' approach useful in the field.
Don't worry about holding small. Look at the target. Close eyes. Shoulder rifle. On target? If not, lower the rifle, shuffle feet and repeat. Ask your body to do it, because the mind is not much help here.
On target? Good. Notice how point of aim goes up when you breathe in? Down when you breath out? Good. Keep breathing (especially important in the field)
my right arm is pretty much parallel to the ground. (Play around with this, raising and lowering of the elbow should cause the butt of the rifle to rotate with your shoulder)
My left elbow is pretty much straight under the rifle, just touching my rib cage.
Both hands grip firmly. I find if I pull the gun into my shoulder with my trigger hand, when pulling the trigger it's much easier to vector the force straight back. I don't wrap my thumb over the stock.
Breath modulates the vertical component, so I try to get a sense (as I breathe) of how full my lungs are as the crosshairs move over the target. Im not even thinking about horizontal - just vertical. Say I cross centre at 60% lung capacity. I'll try to stop the next exhale at 60%.
At this point my finger comes off the guard and onto the trigger. Now it's just a matter of getting the desired sight picture and breaking the trigger without moving the gun. (Isn't it always).
I don't spend much time snorkelling these days, so when I hold my breath I have about 4 seconds before my heart rate starts to increase and blood pressure climbs. As a result if I don't make the window, I'll lower the rifle for about 10 seconds and start again.
I'm by no means an expert, but I can consistently break clays at 100yd (facing not flying...), I have logged more than one offhand group under 2", (though shoot enough of them and it's bound to happen I suppose)
Tips;
-dry fire, a LOT. Get onto target, break the shot without blinking, and a real bullet would land where the crosshairs were after the click. Do it at home, every day if you can, even if it's only 5 or 10 pulls of the trigger. Frequency over volume.
-aim small miss small; use the smallest target you can find for dry fire 1/2moa-2moa, distance doesn't matter.
-use binary targets when going hot. Don't worry about groups. Balloons are pretty good for building confidence. Inexpensive, and you can blow them up to the size of a deer's vital zone.
-fitness. Good cardio health will help your shooting. It will help a lot of other things too.