Here's how: Get a .22. They're inexpensive to buy, new or used. They don't kick. And 500 rounds of ammo sets you back about $9 (compared to about $400 for .270 and about $70 for .22 mag.). Ideally, you want a .22 that's as similar to your regular deer rifle in weight, feel, action, sights, and trigger pull as possible. That said, it doesn't have to be a perfect match to vastly improve your shooting.