Interestingly, the lauded Q3131A ammunition from Winchester is actually slower, for a given barrel length, than even Russian 7N6 ammunition. Bulgarian 7N6 ammunition, which is fairly common stateside, produces significantly higher velocity, and even more energy than the "gold standard" Q3131A.
This is NOT intended to assert that 5.45 is "better" than 5.56. Whether either cartridge is better than the other is determined by the context in which "better" is relevant. e.g., I consider 5.45 to be a superior cartridge design, but for defensive use, from AR-15s, using civilian ammunition, the .223/5.56 is clearly better (Black Hills doesn't make a Barnes 62gr TSX load for 5.45). However, the widespread opinion that 5.45 is "anemic" compared to 5.56 is wrong, and mostly based on inexpensive civilian 5.45 ammunition, versus hot M193 fired from 20" barrels. All else being equal, the two cartridges are highly comparable.
http://196800revolutionsperminute.blogspot.de/2012/11/m193-vs-7n6.html
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