So, I've always wondered:
If the sling provides no advantage for standing then why is it against the rules of High Power shooting to use a sling in that position?
I'm not disagreeing with Col Cooper, I'm having a hard time believing the NRA would put in a rule just to be helpful.
You'll have to ask the NRA. While you're at it, then ask them why they DO allow it for sitting, kneeling, and prone.

Maybe they're just trying to save you a bunch of trouble and effort for nothing, and/or maybe it's a safety issue in the standing position.
But do your OWN tests and see if the "hasty sling" does anything for YOUR offhand shooting. You never know, it just might. Hell, I know that it does nothing for mine, and I
still do it sometimes, just because it FEELS like it's helping, or should be.
