I don’t claim to be an expert and I have very little experience with 6.5 Grendel and .224 Valkyrie, but I have noticed some things in comments that I don’t quite agree with. Below are some generalizations based on the majority of rounds per caliber from what I have seen.
5.56/.223
-fast muzzle velocity
-poor ballistic coefficient bullets
-good energy out to 200 yards with best bullets, 100 yards with most bullets
-easily affected by wind drift
-flat shooting to medium range (500 yards approx. compared to other cartridges)
-bullets have poor sectional density
5.56/.223 is a great plinking round, inexpensive and plentiful. Its short and light bullets don’t do it any favors at distance with wind, energy, and bullet drop; but its velocity makes up for this in the short to medium ranges. Though hunting bullets are designed for the caliber to even take deer, the low energy and poor sectional densities of most bullets make this caliber more suitable for varmints. Lowest recoil out of all the rounds talked about.
.224 Valkyrie Starts out fast, good ballistic coefficient bullets,
-fast muzzle velocity
-good ballistic coefficient bullets
-good energy out to 300 yards with best bullets, 200 yards with most bullets
-less affected by wind drift
-flat shooting to extreme long ranges (1000 yards approx. compared to other cartridges)
-bullets have okay sectional density
.224 Valkyrie is a great long range round for target shooting. Its long slim bullets are less affected by wind, shoot flat, and hold energy better than its stubby .223 cousin. Though it appears to have decent energy at close range with okay sectional density needed to get penetration on deer sized game, I have not seen any loads made for deer hunting and the .22 caliber bullets don’t do it any favors in this hunting category. This is meant to be a fast round and so it benefits from long barrels to get it that velocity. The perfect varmint caliber and fun long range gong ringer.
6.5 Grendel
-medium muzzle velocity
-good ballistic coefficient bullets
-good energy out to 400 yards
-less affected by wind drift
-flat shooting to long ranges (800 yards approx. compared to other cartridges)
-bullets have good sectional density
6.5 Grendel is a good long range round. Though its velocity is not impressive, the good ballistic coefficient bullets are less affected by wind, hold energy very well, and shoots pretty flat for a medium velocity round. The good energy at distance and good sectional density make the Grendel the best deer size hunting caliber in the AR-15 platform, yet it feels at home hitting steel even out to 1000 yards or hunting varmints. Most people believe the Grendel needs a long barrel, but this is not the case. It is not a caliber that needs those high 3000 fps velocities to do its thing, so doesn’t loose much in barrels 16 inches or shorter, that’s why you have been seeing them more often. A bit more recoil but this is your do it all AR-15 round if you ask me.
.300 Blackout
-slow muzzle velocity
-okay ballistic coefficient bullets
-good energy out to 200 yards with best bullets, 100 yards with most bullets
-easily affected by wind drift
-flat shooting to close ranges (300 yards approx. compared to other cartridges)
-bullets have okay sectional density
.300 Blackout I am not afraid to say I have fallen in love with. Reasonable priced ammo that is easy to find and a whole lot of fun. It shines with what it was made to do, fire subsonic suppressed rounds or supersonic rounds for a little more of a bang. It is a slow round, but doesn’t need those super long barrels. It feels right at home in a 7" to 12.5" barrel. Sure it doesn’t shoot flat, and the fat bullets are more easily affected by long slim ones, but I guarantee that if you have it properly zeroed, you can hit a man size target from 0 to 300 yards with the same point of aim. Though there isn’t a whole lot of energy behind it, it has a .30 cal bullet for larger wound channel with okay sectional density, and really very comparable to .30-30 before Hornady’s LeveRevolution came out. With the best hunting bullets, I wouldn’t hesitate to take a shot at a deer between 100 and 200 yards. Added benefits, reload from .223 brass and 30 rounds in a standard 30 round AR-15 mag.
Sorry for the long post, just my take on the 4 calibers others have mentioned. Hope it gets people thinking. And hey, if you can have 1 caliber, why not have all 4.