I have been shooting competitive rimfire for a few years now, and have a background in PRS and other centerfire precision and gas gun competitions. I am a huge fan of PRS Rimfire, and I encourage anyone interested to get into it. You have gotten some solid advice, so I'll try to avoid repeating anything unless I think it's something important to reinforce.
1: Ammo selection is the rimfire equivalent of cartridge development in centerfire. The top .22LR manufacturers (Lapua and Eley) intentionally change aspects of their lots, knowing that different rifles will shoot one lot better or worse than another. You have to find the ammo that your rifle likes. Lots of serious competitors will send their rifles out to the Lapua test centers to get matched with whatever they have on-hand that's the best for their rifle, and then buy as much of that lot that they can. Alternately, you can go to
Killough Shooting Sports and pick up a couple boxes of different lots and test for yourself. I literally order 2,000-5,000 of whichever lot or two works best for me right from the range. They show live inventory of each separate lot, so you can be sure to test lots that are the most likely to have adequate quantity to get you through a season or two.
For performance, I first test at 50 yards (clean barrel seasoned with 20 rounds of whatever lot I was shooting last) looking for 10-round groups to be consistent 0.5" with no fliers. I then test at 100 yards, looking for 0.3 MRAD or better vertical groups. I don't get too wrapped up in horizontal dispersion since wind is a factor at 100 and I will generally not hold or dial for wind during this evaluation. I like to shoot 5 rounds of each lot before going into the 10-round strings just to make sure the bore is getting fouled with the lot I want to evaluate rather than the preceding lot. I will shoot 3 groups of 10 rounds each at 50, and those that pass the 50-yard test get at least 3 groups at 100. I allow the barrel to cool to ambient between lots, and give the barrel a few minutes of cooling between 10-round groups. I shoot the groups in about 90 seconds.
2: Balance is a major factor in being able to stabilize the rifle with minimal physical input. This is the reason that most of us are running around with 1.2" straight barrels in the 22"+ area, with rifle weights over 20lbs. Even with that much barrel weight, a lot of us still need to add chassis weights to get the balance point a few inches forward of the magazine well. This matters because the majority of stages will be shot from a barricade/support of some kind. Prone/bipod stages account for less than 50% of shots taken during these events. Most of my decisions related to changing my rifle are to improve balance (generally meaning adding weight to the front of the gun).
3: With a balanced rifle, you will be able to get through 90% of stages with just one bag. For me, that's a
Shmedium Game Changer with a standard or heavy fill. They work fine as rear bags, and great as positional support bags. If you aren't already familiar with them, be advised that they do need to have some of the fill taken out, as they come a bit "overfull" when new. I remove just enough fill so that when placed over the thin edge of a 2x4 I can't feel the top of the board from the top, through the bag, with the palm of my hand. That's to ensure that the bag is supporting the rifle, not the hard piece of support, and a 2x4 is about the thinnest thing that I'm going to put the bag over with the "tits" down.
4: The optic matters. The 3 most critical things, in this order (to me) are: sufficient elevation travel to be able to put 20 MRAD in elevation without needing to hold (preferably 30), the ability to bring parallax down to 10 yards, and enough clarity to be able to see what I need to see for a correction.
20 MRAD of elevation will ensure that I can cover the vast majority of distances without needing to hold unless I choose to, and 30 will get me out to 500 yards. To achieve this, I have 50-60 MOA in my mount/base combo. Any more than that and I am not sure I would be able to zero at 50 yards without being at the bottom of my elevation travel. I select optics with as much elevation travel as I can get.
Parallax management is a significant part of this game. Since we're dealing with distances inside 300 yards for the most part, and 50-150 for the majority, you're either going to need to be fast on adjusting parallax during a stage, or shoot out of focus/parallax for some targets. Nothing in higher magnification ranges are very forgiving at those closer distances, so it's worth working on both adjusting the parallax between targets and learning what you get away with on being out of parallax for certain distances. Being able to bring parallax down to inside 25 yards can be an advantage, as targets between 15 and 75 yards tend to be very small.
The higher the optical performance, the more you will be able to see. This matters when shooting a tiny little projectile into a berm that has any kind of vegetation on it. Being able to pick up that little puff of anything can be the difference between a 9/10 stage and a 0/10 stage. Similarly, if the target is just hanging out by itself with nothing behind it, being able to visually catch the projectile as it falls toward the target gives you something to work from. Of course, if you just never miss you really don't have to worry about that.
