The .22 conversions available for them tend to be
cranky, unreliable, inaccurate and a beast to clean. There are two
reasons for these problems. One, the centerfire bore is supposed to
have a nominal diameter of .224-inch, while the .22 Long Rifle bore
is supposed to have a nominal diameter of .221-inch. Those three
thousandths of an inch do matter.
And second, the slowest twist in an AR barrel is one turn in 12
inches. A proper rimfire bore has a twist of one turn in 16. The too fast
12-inch twist, combined with the loose bore, means casual
accuracy. (You can imagine what the one in nine or one in seven inch
twist rifling some AR barrels have does to a soft rimfire bullet.)
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