If you're actually shooting a hundred rounds a week:
Walmart ammo $13.97 per 20 x5 = 100 costing $69.85
$69.85 x 52 weeks=$3632.20 plus tax
The $300 you spent on a rifle will matter little.
I take the leech that's bleeding me
Can't stop to save my soul
I take the leash that's leading me