It's my understanding that most fmj ammo doesn't fragment out of the m4 past 90 meters but will fragment out of the 20" barrel out to 250 meters. Anyone have any info on both hollow point and fmj ammo out of both the m4 carbine and the standard 20" barrel.

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Definetly a complicated question that I asked

Yes its a very complicated question.  It also depends on what you plan on using the round for.  A varmint hunting round should perform differently from a defensive round, and a hunting round should be different from either of the first two.

The Big Question to ask: What is the inteded use of the round?
1) if defense, then you want a round that will penetrate at least 12" of denim covered ballistic gelatin.  

 a) Will it need to penetrate glass or sheet steel (important if you are an LEO)?  If yes then you want an bonded core round - not a fragmenting round.

2) If the round is for varmint hunting?  Then you'll want one that fragmenents violently and quickly.  Rounds like these tend to cause shallow wound in humans and are unsuitable for defense.

3) Will you be hunting medium sized game?  If yes then you'll want an expanding softpoint with minimal fragmentation for better penetration and minimal damage of the meat & hide.