castnblast,

"AR mag confines" usually means you cannot load longer than 2.260" unless you use something like ASC stainless magazines which allow a bit longer COL's. It makes a difference when loading the longer, sleeker bullets several guys have recommended. All of that doesn't apply to your rifle.

Don't assume the 40's you have on hand won't work in the 1-8 .223, the ones you've mentioned are plenty tough enough for vermin and normal target shooting. Don't believe the old caution about "overstabilization", it may have been real in the days of poor bullets, but these days it just ain't so.

If you want to shoot larger game and/or long range targets, the heavier bullets others have mentioned are certainly better.

'Four legs good, two legs baaaad."
----------------------------------------------
"Jimmy, some of it's magic,
Some of it's tragic,
But I had a good life all the way."
(Jimmy Buffett)

SotG