As with most in the military, they shoot...freehand / offhand ! Only the guys with the heavy guns get tripods.
Also, as with most everything in nature...it takes a little work, practice or, training to learn something new.
All I do is shoot freehand also. No outside stick help. It's a good feeling when "I"...can hit what I'm aiming at, using only my skills, or the lack of.
I'm rapidly coming up on 72 years old. One thing that really bothers me...I...used to be... a LOT better when I was younger. Shooting both (firearms) rifles and pistols. It gets annoying when the barrel moves around, now, vs. when I was young. The barrel used to stay where where I put it. Nowadays, I need to "anticipate" when the barrel / sight is going to be where I want it to be to pull the trigger.
I actually do ok when I concentrate, but occasionally, it's just not worth fighting old age, but I have to keep trying !
As the saying goes..."Don't let the old man in !"
One thing that I've found, is my support hand while shooting rifles, I keep close in. That is close to the trigger guard, rather than way out by the end of the gun like some do. I've found that it's easier to keep the gun steady with my support elbow resting on my chest, and my support hand, open, palm up, located just ahead of the trigger.
Keep practicing... Ultimately, it IS very rewarding when JUST..."you and the gun"... hit your target.
Mike