If you're already an ATA member....talk to your club rep for the ATA shoots - they will be able to tell you everything you need to know.
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There are sub classifications based on age.....and then it depends on your score averages.
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Shooting in the low 20's is a good starting average.../ but if you expect to win events, you'll need to really work at it and get your averages up in the 23 plus range pretty quickly..../ but 20's and a 21, show that you have some consistency which is good..../ but then you have to get that average up to a 21...then a 22...and then a 23....and hold it there...
Set goals ....say to shoot in the low 90's ( 4 rounds at 23 will give you a 92 )...but let's say you want to shoot that 92, with no one score less than a 22.../ and while the difference between a 22 and a 23 is only one bird....there is a huge difference between recording an 88 and a 92...
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Talk to your local rep...they will have shoot results for the last 2 or 3 registered shoots...and see what they gave for prizes, money, etc...and what it will cost you to enter the tournaments. The option payouts get kind of strange....depending on which shooters got into which options.../ so be careful on that stuff - it can get expensive !
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Going to a "State Shoot" is a whole different level of competition...you're jumping into a big pond now...but your state ATA will have a website, with the entry forms, cost ...and prizes to be awarded..