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For general purpose combat use with 1/7 twist barrels from 0 to 600 yards, I would choose one of the combat proven 5.56 mm (ie. 5.56 mm NATO pressure loads, not .223 SAAMI pressure loads which run about 200 f/s slower) heavy match OTM loadings: either the Hornady 75 gr TAP (#8126N) using the OTM bullet w/cannelure or the equally good 77 gr Nosler OTM w/cannelure loaded by Black Hills, followed by the 77 gr Sierra Match King OTM-which, while exceedingly accurate, offers slightly reduced terminal effects. If your expected engagement scenario is at more typical LE distances, say out to 200 yards, then the .223 SAAMI pressure loads are fine. The experimental BH loaded 100 gr OTM exhibits impressive fragmentation, even at relatively low velocities, however, their trajectory is like a rainbow-definitely for use under 150 - 200 yards.
NOTE: For general purpose LE use, if stuck with 1/9 twist barrels, the heavy 70+ gr match OTM loads are not universally accurate in all rifles and the 69 gr SMK OTM, the 68 gr Hornady OTM, the Winchester 64 gr JSP (RA223R2), or one of the new Federal 64 gr TRU (223L) JSP, Hornady 60 gr JSP, or Nosler 60 gr Partition JSP's are the best choices to most likely run accurately in the majority of 1/9 twist rifles. You are screwed with 1/12 twists, I would probably choose the 55 gr Federal bonded JSP load (Tactical--LE223T1 or identical Premium Rifle--P223T2) in order to ensure adequate penetration.
The best LE .223 loads for intermediate barrier penetration are the 62 gr Federal bonded JSP Tactical (LE223T3) and the similarly performing 55 gr Federal bonded JSP load. The Swift 75 gr Scirocco bonded PT and 60 gr Nosler Partition JSP bullets are also good choices. The all copper Barnes TSX bullets can work reasonably well, although the expanded "petals" shear off sometimes when penetrating glass intermediate barriers. None of the OTM bullets, even the heavy 75 - 100 gr loads, offer acceptable performance through automobile windshield glass. FWIW, contrary to what many believe, 62 gr M855 FMJ also is not very good against glass. For military use, the M995 AP is the best choice for vehicles and glass.
If a short barreled 5.56 mm weapon, such as the Colt Commando, LMT/Crane Mk18 CQBR, HK416, HK 53, HK G36C, etc… is used with a 1/7 twist barrel, the 75 gr Hornady OTM, 77 gr Nosler OTM, 77 gr SMK OTM, and 100 gr BH OTM loadings offer acceptable performance, as do the LE Fed 55 or 62 gr Tac bonded JSP's and the 60 gr Nosler Partition JSP bullet; for LE with a 1/9 twist, stick with the Fed 55 or 62 gr Tac bonded JSP's or the 60 gr Nosler Partition JSP bullet. Remember, with barrels under 14.5”, the effective engagement distance is significantly reduced compared to the longer barreled carbines.
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