What you need: strapping tape or electrical tape, Philips head screw driver, rifle
What to do: Unscrew the bolt first of all. Then, reinforce the area from three inches toward the barrel from the bolt to the grip (skinniest part of the rifle) with tape. There's no set technique for this. Just go slow and avoid air bubbles. Then get a feminine pad or toilet paper to cushion the butt and barrel tip and tape from barrel to butt! Taping is very important if you want to prolong the life of your rifle. Then screw the bolt back onto your rifle.
TIGHTENING THE STRAP:
What you need: pliers, Philips head screw driver, rifle (with leather strap)
What to do: Hold the bottom of the strap fastener in place with pliers and then use the screw driver to unscrew the strap fasteners. Then tighten as desired and rescrew! I've heard of someone getting rid of the strap fasteners in entirety and just holding the straps together with electrical tape.
Like the sound the rifle makes when you catch it? Want more "snap?" Then tape pennies to the inside of the strap. I got this from The Colorguard Site. (Check my links.)