Re: Positional Shooting
First, take the sling out of the picture, or use it in the parade position. Get a data book, and plenty 200 yard reduced course targets for shooting at 100 yards. These will be marked SR-1. Now, in a 50 minute period, you'll alternate dry and live fire on a single target placed at 100 yards, plotting both dry and live calls on a 200 yard target page from the data book. Only after the 50 minute/20 live round period will you observe and plot the actual strikes in data book. BTW, don't set the target too low or too high, you want the bore reasonably horizontal.
A corollary between plots and strikes will quickly address your skill, no matter the actual placement. A good corollary means you need nothing more than a sight adjustment. No corollary, then you could have a multitude of problems; but, if you're getting good results from the prone position, assuring basic marksmanship concepts have earlier been mastered, work on muscular relaxation, adjusting NPA until the sight wobble is confined to the bullseye. Keep the sight in focus, not only to have exact recognition for where the barrel is pointed but to fool the brain into thinking the bullseye is at the front sight. This inspires confidence. After all the target is only inches away, not something way out there that just looks too small to hit.
For starters here's a tip, bring the rifle's stock to the head, not the head to stock. The higher the position the higher the stock. This is where the position begins, understanding, of course, that you've already placed your feet shoulder width apart and somewhat perpendicular to target. Starting here makes it easier to adjust NPA to perfection, which is the whole thing to the standing position. Also, maximize bone support, inverting the elbow of the non-firing arm onto your body, if possible. Control sight height from the small of your back and adjust NPA by moving the whole body with your feet.
I fear without a coach you may still not get a proper start with all of this. Kinda like you're on an airplane and the pilot parachutes, leaving you to fly the plane.. and land it. What I'm saying here is that you may crash, trying to do this without some help. Thing is, a highly qualified coach could get you up to speed on this in less time than it took me to write this post.
Take Kraig's advice and get a copy of the USAMU's Marksmanship Guide, or go to the AMU's web site and download BRM classes. These files are apparently corrupted, but there's one slide which shows the standing position with instruction on building it. This may help you, you know monkey see, monkey do sort of thing.