For 223, my testing is limited to a little bit of clear ballistics gel from a 22" upper and a few coyotes. "Other bullets" is a lot of 45, 40, 9mm projectiles into clear ballistics gel at speeds ranging from 750 fps to 2600 fps, and somewhere in the neighborhood of 200 whitetail that I've either field dressed or helped field dress over the past 40 years. We've used archery equipment, shotgun slugs, ball and patch, modern inlines, 44 mag pistols, various hand cannons, and various high powered rifles (.270 Win, 6.5 CM, 6.5 Grendel, 7-08, 308, 300 BO, and others that I've since forgotten about).
On the ballistics side, my testing was done for 2 different reasons. The first was a series of tests with a Savage 10ML-II muzzleloader using saboted 45cal projectiles. At the time I was using an ordinary 250gr SST and pushing it at 2600 fps. I'd shot everything from small yearlings at 20 yds to reasonably sized bucks at 150 yds with "good" results, but I was surprised that the projectile never exited. Prior to buying the savage, I had hit a couple of deer with some 140gr Dead Center (pure lead) projectiles running 2200 fps at the muzzle and they did not maintain their course on impact. I didn't think much of it at the time (2002), but around 2005 I was hearing of guys making good hits on big bucks with the 250gr bullets and not recovering them. I fired every 250gr (2600 fps) and 300gr (2450 fps) projectile I could find into some clear ballistics gelatin. I notice that the 250gr cup and core bullets would frequently want to veer off course after flattening out about 4" into the block where as the 300gr bullets all gave VERY consistent wound channels that were straight and 22" to 24" long (the 250s were 17" to 19" when they stayed in the block). The exception was the 245gr Barnes which also stayed straight and I THINK went closer to 23" deep. I reasoned that if a cup and core bullet totally flattens out (like the 250gr always did) they destabilized and often veered off course in the gel. On a big deer, if the bullet expanded significantly before striking any kind of bone, this could happen on an animal. Even though I never had an issue, I immediately switched to a 300gr SST and have enjoyed pass throughs ever since. The other thing I've noticed is that with the 250gr, there was a LOT of meat damage on the entry side, but not as much on the exit side (bullet and jacket were always laying under the hide) where as with the 300gr I get a lot of meat damage on both sides due to the retained momentum. I still use it for our ML season, but for our firearms season I've gone to a 6.5 Grendel and a 300 BO.
The other ballistic gel tests were done to determine what projectiles expand consistently when fired from the shorter barreled pistols that are common today. My wife had bought me a 45 Shield against my advice. Turns out I love it. I don't recall the 9mm and 40 info, but if you're using a short barreled 45ACP, you REALLY need to use something that fires a Barnes DPX projectile. Of the 50 rounds that I fired that were loaded with one of these projectiles, most of it was through denim covered gel, and all 50 expanded and gave adequate penetration. The ONLY other thing that came close was Critical Defence which I only tested 10 rounds of. 5 in bare gel, 5 in denim. They performed well, but only expanded to just under 5/8". Not terrible, but that's not a lot of expansion for a .452 bullet.
When I'm talking about shooting deer in a bean or corn field, I'm talking about shooting them at farther distances. Shots in the woods are generally under 100 yds, but its pretty easy to reach out past 300 yds when sitting over the edge of a large field. This doesn't, or shouldn't apply to most hunters. I'd estimate that 80% of the deer hunters I've met struggle to hit a pie plate at 150 yds with a centerfire rifle. I'm not sure why that's the case, but it is. For me, 200 yds and under is a boring run of the mill shot that requires very little skill or ballistics knowledge/experience. I'm not saying that to brag, I'm just giving it as a reference point. If I'm setting on the edge of a field that's 800 yds long x 500 yds wide, I'm going to be set up to effectively reach half of the field. No one said that a .223 is a good option for this scenario, but you had mentioned 400 yds and I think that number should be cut almost in half to ensure the bullets impact velocity/momentum/KE are high enough that the bullet performs as intended. I'm concerned that the lower velocity are farther distances can result in inconsistencies in performance depending on what bone structure is impacted on entry. I will concede that there could be a few projectiles that happen to be optimally designed for this application and would work well at farther distances, but I'm not aware of those. If I were looking for something like that, I'd probably look into an expanding monolithic from Maker Bullets. They, along with Cavity Back use a softer copper alloy that expands and lower impact velocities. I use CBs 105 MKZ in my Grendel and run it at 2800 fps. I had a clean pass through on a mature buck at 297 yds quartering hard away from me. I'd estimate well over 30" of penetration which was enough to put a nice size hole in his heart before exiting through a rib just in front of the far shoulder. For me personally, if a big buck is an option, I would want at least a 6.5 Grendel or 6.8 SPC. The margins the give do not make up for inaccurate shot placement. Rather, they increase the potential shot opportunities.
