Sorry for the long post but I hope this helps you with the next step along the path to finding out just how accurate your 22 LR rifle might be. Don't get me wrong, I am not saying you shouldn't shoot bulk ammo too especially for plinking, but if you are interested in finding out just how accurate your rifle is the following might help.
I suggest you try several different sub-sonic ammos. As several have already posted, every rifle has its own favorite ammos and you can't really predict which they might be.
I believe all of the economy ammos (bulk ammos) are higher velocity partly because they cycle most semi automatic rifles. Your single shot rifle doesn't need to worry about having to cycle the semi-automatic bolt so you don't need the inherent inaccuracy that comes with higher muzzle velocity.
I have found subsonic ammo - that includes all match ammos - are significantly more accurate than ammo whose velocities exceed 1150 fps at the muzzle. The sub-sonic ammos are under the speed of sound at the muzzle so they don't have to pass through the sound barrier from muzzle to the target so they don't wobble when they transition.
I tested 25 subsonic ammos versus 25 ammos that had muzzle velocity ratings over 1150 fps and found that across 10 different rifles the subsonic averaged 0.575 and the higher velocity ammos averaged 0.753. The test measured 5 round groups at 50 yards outdoors and included 6356 groups. Needless to say, the test was run over several years and is still on-going as new ammos appear on the market.
Across the 10 rifles (4 bolt actions, 3 10-22 clones and 3 Kidd 10-22s) all but one rifle shot its 5 favorite ammos under 0.5 inches (all with subsonic ammos). Five of the 10 averaged under 0.4 inches with their favorite 5 ammos. The one exception, a bolt action, has averaged 0.512 but it is a newly acquired rifle and hasn't finished testing across the entire 50 ammo set so there is still hope.
The overall average of all groups versus the average of the 5 favorite ammos should give you an indication of what the rilfes shot with the other 20 ammos to average 0.575 overall. It just proves every rifle has its favorites and even among some pretty expensive match ammos, you might not find a favorite for your rifle.
All 10 rifles seemed to like Wolf Match Target or Match Extra (SK Standard Plus is the same as Match Target). Match Target and SK Std + ammo are about $5 a box so they are a good choice to take the next step toward finding what your rifle might like. The quality varies a bit from lot to lot don't be surprised if the first box isn't a world beater.
Wolf Match Target and SK Rifle Match seem a bit more consistent from lot to lot and are a bit more expensive, but maybe worth a try too .
Most of the 10 rifles liked Lapua Center-X qand Lapua Midas Plus. About half liked Eley Match and a couple shot it better than any other ammo.
Just as a point of comparison, only two of the rifles shot Remington Subsonic around 0.6 inches - most didn't. I think your rifle may like that ammo regardless of its velocity so you are fortunate that you have found a good shooting ammo that won't break the bank.
None of the 10 rifles shot Federal Target, CCI SV or Green Tag subsonic ammos really well but a few shot it reasonably (around 0.5 inches). The higher velocity CCI and Federal ammos shot like all of the higher velocity ammos - a few shots touching and one or two flyers/drops that are very characteristic of high velocity ammo when it makes the sonic velocity transition.
From my experience, all of the economy ammos (bulk ammos) are higher velocity partly because the higher velocity ammos cycle most semi-automatic rifles and pistols without problems. Your single shot rifle doesn't need to worry about that so you don't need to pay the accuracy penalty for sonic velocity transition.
The sub-sonic ammos are mostly match or target ammos so they are a bit more expensive but you are generally paying for some bullet quality checks and some accuracy tests that qualify ammos for different price levels and box stamping.
For example, the best Eley ammo is made on the same production line as two of their lesser priced ammo. If the production run meets the quality checks, it gets put in red Tenex boxes, if it doesn't meet the highest test but meets the second level test, it gets put into black Match boxes, and if it doesn't pass either, it gets put into light blue Team boxes.
That is what you pay a premium for and Tenex ammo is super expensive and Match ammo is just expensive.
Lapua X-Act, Midas Plus and Center-X have the same kind of quality checks and criteria as well as mega expensive, super expensive and expensive pricing levels as the bullets drop through the quality filters.
BUT if you are shooting at 100 yards, you find that the extra quality is worth it and pays off with under 1 MOA groups.
liff