Kinda new, quick question……what is the difference between all of the aac 556 ammo? I understand grain. There is the basic 55 grain 556, then AAC 5.56 NATO 77 GRAIN SIERRA TMK, then AAC 5.56 NATO AMMO 77 GRAIN SIERRA MATCHKING HPBT W/ CANNELURE, then AAC 5.56 NATO 75 GRAIN BTHP MATCH W/ CANNELURE & JAG HEAD STAMP.
I shoot well with the regular 55 grain out to 300 yards and have been told I need to go to a heavier grain for say 400-500 yards.
I got a few boxes of the heavier grain aac and a few boxes of hornday and remington.
It sounds like they make some of their own bullets, don’t they? I’ve been looking to pick up some more 77gr and there are a few different offerings. Obviously if it’s says sierra or matchking I get it, but what about the others?
@Bob0 since you say you’re new, may I assume new to shooting in general, or to the forum? Or both? I apologize in advance if I’m answering this more simply than you need.
Generally speaking, yes, 5.56 longer range shooting will be more accurate with heavy for caliber bullets, such as 75 or 77gr. The lightweight bullets such as the common 55gr can get there, but often with less accuracy. 62gr is common because that’s what military ammo is, such as the M855 green tips and similar. It’s a decent compromise to get the high velocity 5.56 needs for best terminal performance, while having good legs for distance, too. The reason for this better long distance accuracy from heavy bullets comes from the greater mass behind the same frontal area. This is the sectional density (SD) which also lends itself to having a more aerodynamic shape and higher ballistic coefficient (BC). Then the bullet manufacturer can add in features like a boat tail which further improve the aero design. A 55gr bullet is short, fat, and has a flat base. Not the slickest shape for flying far.
Also, the twist rate in your barrel matters greatly. The heavier the bullet, the faster twist needed to properly stabilize the bullet in flight. There’s tons of great resources online to calculate optimal twist based on bullet weight and expected muzzle velocity. Modern 5.56 rifles are usually chambered in 1:9, 1:8, or 1:7. 1:7 is mil-spec so it’s likely the most common. If you have this you’re good for pretty much anything except super lightweight 40gr varmint or frangible ammo, but those are off topic.
The design of the bullet is well described on the Sierra website, and what you should pick will depend on what you want to do. The MatchKing series, for example, are fantastic for accuracy, but not always as great for terminal performance. Not that they’re Nerf guns, but it’s something to consider. The plastic tipped bullets are probably better there since the tip is designed to allow for better aerodynamics while still having a more open front hollow point area.
Finally, your rifle is unique and will like some ammo more than others. Buy a box of each to test them out, and have fun shooting!
With the exceptions of relatively common M855 62gr green tips or the handful of far more rare options, the vast majority of ammo will have nothing but lead and copper, making them range safe everywhere. All of the options you listed in your first post are copper jacketed lead core bullets. The increased mass of the 77gr bullet versus a 55gr bullet is because the bullet is longer, not because of different materials.
For Open Tip Match (OTM) rifle bullets the open tip is a byproduct of the manufacturing process. You can google for examples and videos, but it really doesn’t have a purpose and doesn’t do anything upon impact. These bullets tend to be very accurate because the manufacturing process itself makes more consistent bullets. If it were a Hollow Point (HP) then it is designed to open up when hitting tissue upon impact.
It’s true that the open tip makes for a slightly higher drag bullet. If you were to look a bullets designed for extreme long distance shooting they are usually machined monolithic copper bullets with an extremely sharp point. But these very sharp tip bullets have feeding issues with what is basically a needle point catching on the internals of the rifle, so they have to be loaded one at a time by hand. Deformation of a sharp tip can have issues with balance of the spinning bullet as well as airflow around that bent nose. So the bluff nose makes these more common bullets a far more user friendly choice. For practical purposes, the open tip isn’t enough of a difference to make a difference.
Here’s a website with an exhaustive description of many, many different types of bullets.
