Unless those scopes are rated for airguns, don't do it; you'll break them.
As I said above, Crow Mags will be marginal, at best, on game larger than squirrel and rabbit. You probably won't get the penetration you need, and accuracy won't be that great outside of 15-20 yards. Anything beyond that, use domed pellets. Find the one that shoots most accurately in your rifle by buying a variety pack. Skip Gamo pellets; they almost never shoot well in anything. Same for Daisy.
As for the ongoing accuracy problems, is the gun broken in yet? Have you got a couple hundred rounds through it yet?
I don't want to sound elitist or condescending, but about the best accuracy you can hope for from a Nitro Venom Dusk or most of the Chinese-built springers from Crosman or Gamo is 'acceptable' and even then, it is often only at close to medium range. They're just not high-end airguns, and they tend to lack the careful production and finishing that is directly related to accuracy. They're cranked out in a Chinese factory by the thousand. The bores are not well finished, polished, or even cleaned. Scope rails are often not straight. Triggers are usually terrible. They do look nice, often have nicely-shaped stocks, and almost always have very high published velocity. But quality and accuracy are their last priorities.
I'll give you an example. I have what I consider a high-end Chinese airgun, a Stoeger X20. Probably about the same power level as your first gun.The stick is great; sharp checkering, a nice re-settable safety. The trigger was terrible, I upgraded it with a Charlie da Tuna one, which is still heavy, but breaks cleanly and predictably. It honks when cocking, because the spring is rubbing somewhere inside. It has cheezy fiber optic sights that give a nice fast target acquisition in low light, but are impossible to shoot a tight group with. They're not replaceable with anything decent, other than a scope. It has many hundreds of rounds through it, and shoots pretty accurately, but still not even quite up to par compared to a typical box stock European springer.
My advice is to return or sell that Nitro Venom Dusk and save the difference to get something decent. For your use, something like a Beeman R9, Weihrauch HW80s, HW50s, or Diana 36 would be great. Something that has been put together with some attention to detail by a company that cares about its long-term reputation.* Then, pop a decent scope on it. These are not the same as simple powderburner rifles. There are a lot more moving parts that have to work well in unison to make an accurate gun. You can buy a pretty nice, accurate 22LR powderburner for a few hundred bucks, and even $150 will buy a nice used one. Even a lot of the super cheap ones shoot well. (thinking of the H&R single shot shotguns and Marlin bolt and semi-auto 22s) That price is just the starting point for a good quality air rifle.
Lastly, try to avoid the mentality that "it's just an airgun, I don't want to spend that much." They end up being just as much fun as powderburners, and a lot cheaper to shoot, in the long run. Not to mention the fact that you don't always need certain designated places to shoot them. Back yard, basement, garage... these are all fair game for airguns.
Let us know the general area where you live. Maybe a member local to you will let you try his arsenal and open your eyes a bit.
* When Crosman started to ruin their reputation for quality by cutting costs, they bought the Benjamin and Sheridan brands to reassure customers that they still make something of quality. Daisy did the same with Winchester for their springers.
