hi
@Varminterror &
@Sunray,
SAAMI doesn't apply to 5.56 ammunition. CIP is closer but two different things. Some makers might indicate the 5.56 or compatible label for the chamber selection.
With high performance ammo we might refer to it as 223 but many times we are talking about 5.56 and compatible rifles and carbines.
Many times one wins ballistic coefficient with the extra grain but they are not necessarily related.
All other things being equal a tad extra grain gives additional ballistic performance in the air w/o significant loss in speed at the muzzle. (lets say many 77 or 80 gr vs. a 75gr or 70gr bullets).
Weight might give an indication but in reality construction, material and shape is what determines performance and also the required twist as well as the MIN and MAX length
that is what really matters in terms of being able to load from an AR magazine and shoot from popular rifles. You have lighter bullets that require a faster twist than heavier ones.
One has plenty of 80gr and 77gr bullets that work well from AR magazines, 1:8 twist and perform really well including top quality loaded ammuntion.
For example the amazing black hills MK262 mod1 with 77gr that is effective for soft targets in combat all the way to 600-700 yards.
Our MK262 produces about 100fps more than the IMI counterpart and amazing speeds not just from SPRs but 16" and shorter barrels. Clocking 2750fps avg. from a 16" with 77grains
is significant and, if that was not enough, they released the 5.56 77gr TMK that does even better in terms of speed and ballistics. The ballistic coefficient of the TMK can be rounded
up to .415 corrected. There are also the 75gr Hornadys and others that are also nice for long range work whether is target, hunting or tactical and many of those loads can get supersonic
to 900 yards and even 1000 yards with ideal conditions even shot from a 16" and ideal from a national match or tactical 20" barrel. They all work with 1:8 twist and some 75gr with 1:9 twist
as recommended by manufacturer although one might choose an extra turn depending on other considerations. But when you look at the speed on the target you see those 77gr and 80gr
come on top. Not by much but this normally translates in more penetration and letality so for certain targets one might choose a heavier bullet, that will also buck the wind a tad better.
This is the 77gr TMK tested from a 16" SI-Defense/arp AR. 555ft ASL. Temp.20C. 10mph. From a 20" barrel expect 2800fps+ give and take.
One has plenty of good performers in the 75gr-80gr with the advantage going to the 77gr and 80gr in terms of externals and terminal ballistics.
There is also the advantage of having extra sectional density and momentum on the target (not energy, two different things). Even not a lot it scores for you.
In terms of terminal ballistics the hpbt, TMK and such behave pretty similarly with 2-3 inches of penetration before fragmentation and they do that with broad wounding
and even a slower speeds therefore avoiding pin hole wounding tipical of other bullets including bonded and solids. They work so well that they are ideal for
long range coyote hunting (like the 80gr amax) and will drop a coyote at 600 or 700 yards if one can hit them. Some lighter bullets cannot get there with enough speed and momentum
to be consistent.
We have plenty of bullets from berger, lapua, nosler, sierra, etc.. in the 77gr-80gr between 1.030 to 1.070 that fit the AR magazine even when loaded at minimum 2.26 coal although many
people reloading are going to take advantage of modern magazines for longer coal or whatever works best depending on freebore situation.
We even have a barnes 85gr match burner that can also be shot from AR magazines.
But when we get into the VLDs like the Barnes and hornady one jumps quickly into the long bullets from 1.110 to 1.116" and long ogives that makes it impossible to load them into AR
magazines even some of them at max coal of modern mags.
If one wants to reload, with careful selection of brass, bullets and powders one can really stretch the capabilities of the 223. The modern 223 Remington shoots flatter and longer than countless
other AR15 cartriges even some popular ones and many times does that with a pretty affordable budget not just from the initial equipment perspective but total TCO and something to consider if one likes to shoot a lot.
If one reloads the 223AI is another great round that will give amazing performance when loaded from center stack magazines up to 2.45 COAL, something the specialty user and reloader is going to like. Same as the 6mmx45-L and 6mmTCU with 105grains goodies.
