Well.... yes... this might work, assuming it is high enough for your 50mm scope. This is the first time I have ever seen a 30mm ring sold with 1 inch inserts! Yes there are adapters, but I have never seen the ring sold with the adapter and all for under $7. I am assuming your Bushnell is a 1 inch scope and not 30mm. This NCStar is a VERY cheap Aluminum ring.
That 50mm scope is large, and might need extra high rings. Many might suggest that since this is a tall, heavy scope, to buy the Weaver adapter base and go with a quality ring. For a rimfire this isn't absolutely necessary, but it still isn't bad advice to go the Weaver base route.
Suggest you look at these two links and estimate what kind of height rings you will need.
http://www.midwayusa.com/midwayusa/staticpages/charts/ring_height.htm
http://www.midwayusa.com/midwayusa/staticpages/charts/ring_height_comparisons.htm
Do you have a budget that you must stay inside?
Here are all of
Midways rimfire rings. Quality rings would be Weaver Grand Slam, Warne (steel), most Leupolds (not those $10 Aluminum Leupolds), Burris (steel), BKL (Aluminum).
If you want cheap, consider Walmart (also Gander Mountain/Dicks/local sporting goods store). They might have some cheap Aluminum 3/8 inch Simmons/Weaver/Leupold/etc in HIGH for about $10. BTW, aluminum does not necessarily mean poor performance or design. BKL has a reputation of making some nice quality Aluminum rings but they usually start at about $25. Most of the better rings are going to cost you at least $25.