Mo,
Remember our discussions about the 10/22 at 25 yards & 50 yards, with scope?
Then taking the scope off & repeating practice at 25 & 50 yards with the iron sights?
Then moving out to 75 yards?
I'm trying to tell you that you have a long way to go, you're not as far along as you think you are, and that 10/22 can teach you a heckuva lot more before you're ready to move up in caliber.
There most certainly ARE other things you can practice, before you continue to waste time, effort & ammunition on that Mosin.
I know you don't want to hear it, but you're just not ready for it yet & this hit & miss (literally) approach you're taking to learning how to shoot is doing more harm than help.
A sling, at your stage of the game, is not needed.
You have iron sights on your Ruger, learn them.
Peep sights are not an absolute need.
The Mossberg "AR22" is a lower-end plinker among the many .22-caliber AR lookalikes & may or may not hold up over the long run.
The one I worked with ran fine except for some mag-related problems with the extended one.
I've heard reports from others with lesser experiences.
It will not do as well for as long as your 10/22 will.
If you have to have an aperture sight, you can find one for your Ruger.
If you have to have a higher-cap mag, same.
The irons already on your Ruger will, if you learn them, translate better to your Mosin eventually, than an aperture, because the Mosin doesn't have an aperture.
I told you before I've shot one of my Mosins into three holes under an inch at 100 yards, with the standard sights on it.
You learn Notch & Post on your Ruger, you can transfer that ability to your Mosin.
You're motivated, I'll grant you that, but you're also impatient & that is not doing you any good at all.
Denis