Exactly. SD/ES is only one component. The other is BC consistency, with some bullets being much better than others.
The difference between a 10-15 SD and a 4-5 SD will be lost points over a match. There are so many variables that come into play, and you rarely get a perfect shot. The targets are getting smaller every year and the time's are going down, giving you less time to build and break a perfect shot.
I have shot both factory and reloads in matches. Hornady Black 140's, Norma/Prime 130, Norma Golden Target 143, Berger 130 AR hybrid and 144 hybrids all in factory loads.
Hornady is some of the last factory ammo I would shoot. The Norma 143 when you could get it for $22 a box, was a steal. I am half way through about 4000 rounds of it, and use it for training or when I dont feel like reloading for matches. The Berger ammo was really good, uses better bullets but the SD was not as good as I would have liked. It was around 12-15, same as the Norma. The real benefit with the Berger ammo is the better bullets, and use of Lapua brass that can either be sold or reloaded down the road. Going from Hornady Black to Berger factory my groups cut in half and downrange was getting much more consistent hits. I have also heard good things about the Sig Ammo shooting SMK's but never seen it in stock in quantities enough to shoot a few matches.
If you invest in good reloading equipment and have the time, you can make exceptional (2-4SD ammo) using the best components for less than $1 per shot. Its up to you if its worth it. Break even will take a long time, but you also end up with some pretty amazing ammo.
The other big thing is when you are still learning, eliminating variables that hinder your progress is huge in getting better. Not fighting gear or ammo issues lets you focus on other things and you know when you miss its not the equipment. Confidence is huge in this game.
Another option would be to shoot 6 arc factory ammo. Will get you down to the 6mm class bullets to reduce recoil. They are cheaper and only going to get more popular as DOD adopts this round and starts deploying it. If you have a good custom action all you need is a new bolt/mags/barrel. Could then sell the brass to offset the cost.
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