Hey guys, can't find if this has already been discussed and this is for my own edification.  What are the advantages and disadvantages of each round:

 

5.56/223   55 gr

5.56/223   62 gr

Depends on the barrel twist rate among other things. 

 

http://njgunforums.com/forum/index.php/topic/39010-excellent-article-explaining-ar-barrel-twist-rates/

Ok, so unless i'm reading it wrong 62 gr and 55 gr appear to be very similar.  So are there any advantages to using a 62gr at all?  Why are they called penetrators?

Ok, so unless i'm reading it wrong 62 gr and 55 gr appear to be very similar.  So are there any advantages to using a 62gr at all?  Why are they called penetrators?

Because M855 has a steel core that is supposed to make it a better penetrator. M855 is technically an anti light-armor round while M193 is straight anti-personnel. In practice, M193 tends to punch through helmets better than M855 at <200yds due to velocity. When talking about intermediate barriers like cinder blocks, I feel the difference between the two is moot and if you want to punch through that stuff, step up to .308.

As inexpensive range fodder, either will be fine.  If you are looking for long range accuracy, then you need to do some reading.  There are thousands of articles on the net addressing your question.

Ok, so unless i'm reading it wrong 62 gr and 55 gr appear to be very similar.  So are there any advantages to using a 62gr at all?  Why are they called penetrators?

 

In an attempt to "green" the round they added a steel penetrator.  It isn't superior either, just different.

 

M855A1 is a little different as well, but I've read that it shortens barrel life and I would avoid it.

Stay away from the steel core stuff. There is 62gr ammo that isn't steel cored and some barrels like that better then 55gr, but the steel core stuff is damage to steel waiting to happen as well as sparking and chance of fires. Just say no to that ammo. 

 

62gr soft points are nice ammo if you want to hunt things, but so are all the heavier offerings like 69's, 77s, etc. 

In an attempt to "green" the round they added a steel penetrator.  It isn't superior either, just different.

 

M855A1 is a little different as well, but I've read that it shortens barrel life and I would avoid it.

As part of the M4 upgrade program, the military is considering 70K PSI rounds aka proof rounds to make the M4 more lethal. The M855A1 rounds aren't those but are an enhanced version of M855 that are supposed to be barrier blind and more effective against personnel. Now if they swap to shooting proof rounds, well, let's just say they're going to be buying a lot of bolts and barrels...

I asked this question the other day, didnt really get a definitive answer.

 

Seems like a preference thing but for whatever reason, the 62 grain is always more expensive and it still sells out quickly.

Really it is like every other caliber. 115gr 9mm or 124gr 9mm or 147gr 9mm? The grain weight itself is something you get to decide what you prefer and what terminal and flight ballistics you want. The steel core issue is separate because of the military 62gr ammo has it, and it is something to keep in mind, some ranges actually ban it. 

When talking about intermediate barriers like cinder blocks, I feel the difference between the two is moot and if you want to punch through that stuff, step up to .308.

Working on something now for that but it's not a .308.

 

Having reloaded both time and time again, i see little or no difference.  Only time I change from 55FMJ is when I am punching paper for accuracy, then we step up to 68 BTHP.  Some have now gone on to 75 BTHP.  Varmints get Vmax again with 55gr being about the best overall.