To the OP, do you know what flavor 3 Gun you have locally? Some do not emphasize precision shooting at all and may stay within 100 yards, on the other hand some are all about precision and you may have targets well down range. I think this is a pretty important consideration when choosing your rifle platform.
Even if you're going out there just to have fun, it's way less fun if you end up spraying 90 rounds and never hit anything while everyone else got their hits in 10.
You're about to start walking the "false economy" road. 3 Gun isn't exactly cheap to do even if it's just for fun.