As mentioned above - don't worry about rifle drill practice. Don't waste your money on something for that. The Army will train and correct you on their time and dime.
WRT marksmanship, I have several of the 'not an AR-15' type rifles, and none of them are as well developed as the AR Platform - reliability, durability, accuracy, all come up short compared to the AR.
I will not suggest any of them. Don't waste your money like I have.
I will suggest, as others have, getting yourself a .22 and focusing on the basic skills of marksmanship. Position, hold, breathing, sight picture, trigger control, follow through.
If you do not have a PAL/RPAL, I will suggest buying a pellet gun. The Cadet type air rifle is a good start, and tends to be quite accurate. They have the bonus of being able to be fired indoors, at home. Ideally in a basement or a long hallway if you have one, but do so out of sight of your windows and nosey neighbours. Don't use your webbing or other gear as you shoot - just go bare-bones and learn to shoot consistently. Once you're consistent, you can get good.
The Gun Dealer has a great deal on the Cadet Daisey 953 :
Daisy 953 Cadet .177 Cal | The Gun Dealer
If you want to buy a .22, I'll suggest a Ruger 10/22 type rifle. Semi-auto, reliable flexible, upgradable, reasonably accurate. They're available almost anywhere guns are sold.
