For the fun factor and already having .223 cases and SR primers I'd recommend a 300 Blackout. Brass is made easily from .223 brass, you can shoot any 30 caliber bullet from 110-220 grains, uses smaller charges of slow pistol powders, and low recoil. Rifles can be bought in single shots, bolt actions, AR-15 platforms in 16" carbine length and pistol length barrels. It makes a not too expensive to shoot short range hunting rifle. Lots of shooters use 110 to 125 grain bullets for hunting. I like the .308 147 gr. M80 FMJ bullet for plinking. The 300 BLK. has ballistics close to the AK 7.62x39 round. Most popular powders are H110/Win 296, Lil-Gun, and AA 1680 for heavier bullets plus several other powders are suitable. Just an idea since you already have .223 components. Lake City military cases makes the best converted 300 BLK brass. Not a long range rifle but getting popular for short range hunting. The most important factor is cases are available, inexpensive, and this isn't true with a lot of other specialty calibers. Also in specialty calibers popular bullets haven't been available for long periods lately.