I shot rimfire benchrest for about 18 years. It's a very expensive, ammo and rifle dependent game. Test ammo to see what brand/lot# works best in your rifle and buy as much of that as you can afford, then buy more!
It's very equipment-dependent as well. Rests, scopes, tuners, wind flags/indicators are all very expensive. In some venues, you need three rifles, sporter, Light Varmint, and Heavy Varmint. Then, there's Unlimited!
Each rifle will usually like a different ammo brand and/or lot#. There's also some ammo that shoots like a dream, but will throw one or two flyers in a box.
I finally sold my Unlimited rifle and got out of the game, after on one day, shooting two perfect 250 targets and a 249, with the last shot, a 9. The person who bought the rifle has shot several perfect scores and is ranked 7th in the country. He just spend thousands of dollars for very good batch of Eley.
Lot to Lot, the most consistent ammo for me was RWS R-50, but some lots also seemed to have a flyer or two in each box that would give me an eight or nine.
Wind and mirage are major factors in match shooting. Bench location, usually allocated by luck of the draw, is often critical, especially when there are side earth berms and trees that create weird wind currents.