Quote:
Originally Posted by mannyo747
How ya doin guys, Im a newbie to the AR world and shooting for that matter and was wondering what was the difference between bullet grains i read about 55,62,64 and so forth. I just purchased a M&P 15 sport and pick it up this Thursday. SORRY for being such a noob and please bear with me on my journey.
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Keep in mind that a projectile's weight (grains) is only 1/2 of the equation. The projectile shape is the other 1/2.
"(From left to right) Hornady 40-gr. V-Max; Nosler 50-gr. Ballistic Tip; Nosler 55-gr. Ballistic Tip; Nosler 60-gr. Partition; Sierra 69-gr. MatchKing; Berger 73-gr. Match; Swift 75-gr. Scirocco; Hornady 80-gr. A-Max; Sierra 80-gr. MatchKing; Berger 90-gr. VLD."
Source:
Handloading The .223 Remington For The AR15
(Good Article)
Keeping it simple...
The longer boat tail projectile is more aerodynamic than the shorter stubbier projectile, and has the potential to cover longer distances with better accuracy.
Given that there is a finite amount of propellant that can be safely loaded in any cartridge, there is a point of diminishing performance because it takes more energy to propel a heavier projectile than a lighter one.
The heavier grain projectiles aren't more accurate because of the weight alone, they weigh more because there is more projectile: the boat tail.
I always stumble on this part, so someone please please please correct me:
The lighter projectiles require less rifle twist rate (1:9) because anything faster and the projectile's break apart due to centripetal force (a.k.a. spin themselves apart)
The heavier projectiles can handle more rifle twist rate (1:7) because the additional mass can resist the centripetal force.
The 15-Sport has a 1:8 5R progressive gain rifled barrel, so it's like the Goldilocks of the AR15 twist rates. Not too fast. Not too slow. Good for a wide range of projectile weights. The 1:8 5R progressive gain rifling deforms the projectile less as it travels through the barrel, contributing to a higher potential for accuracy.
So which grain projectile should you use? It all depends on what type off shooting plan to do. For practice rounds, I buy whatever is on sale. I love shooting the super affordable Russian steel case ammo.
I have some expensive Hornady VMax & ZMax ammo I have yet to shoot.
I know I'm over simplifying a bit. The hand loaders here will fill in the blanks for me.
