First, don't be scared to go past that 200 yard mark with a .243, I've killed about 150 deer with mine, I have never felt undergunned and frankly can drop any deer in its tracks when I feel the need....A good 200 yard plus bullet is the Federal Premium 85gr HPBT...At longer ranges you want faster velocity to help the bullet open up, if I remember correctly, that loading is moving faster at 300 yards than a 150 grain .308 bullet is doing at 200...I have killed several with that bullet at 250 plus...Another plus, sight in 2 1/2 to 3 inches high at 100, you'll be 2 1/2 to 3 inches low at 300....

Owning a .243, if I wanted a rifle for elk...I'd go with a regular 300 Mag...Frankly for elk, your muzzleloader would do well....I'd take my .54 caliber flintlock myself....