Maximum Grain Bullets to Use For AR15 guns?

[4Freedom]

Hi, I am wonder what is the maximum grain bullets to use for my DPMS Sportical 5.56 and Rock River Tactial Carbine A4? My Rock River and DPMS has a 1:9 twist barrel.

I also have a DPMS LR-308 . It has a 1x10 twist barrel. I am wondering what is the heaviest grain ammo to use for this as well?

I would like to get Hornady TAP ammo for both my 5.56 and LR-308, but I am not sure what is the best or maximum weight for bullets.

 

[otomik]

for the .223
the 1 in 9 twist is optimized for SS109, thats a 62 grain lead and steel penetrator FMJ bullet. for a regular lead bullet that twist is good for 73 grain bullets.
for the .308
thats a tight twist. the usual is 1 in 12 is good for 168gr. 1 in 10 is rare and I'm guessing it will fire any load with an overall length that can fit in that magazine and then some. 1 in 10 is the twist you usually find on a .300win

 

[Swampy]

4Freedom,

YOur 1-9" twist .223 AR will stabilize anything up to 69 grains just fine. Some 1-9 twist rifles will do OK with bullets of 75 grains... some won't.

Your 1-10" twist .308 AR will be fine with any bullet up to 220 grains, BUT the .308 case is low in powder capacity for bullets that big. Trajectory will be close on rainbow shaped at longer distance. Optimum velocity in the .308 case tops out with bullets at about the 175-180 grain size.

Best regards,
Swampy

Garands forever

 

[4Freedom]

Thanks for the advice, sorry I lost this thread cause I was away for few dyas. Do you think Hornady TAP ammo would be a good choice as match grade ammo to store in worst case scenarios. I am looking for some great expanding type of ammo to use for defense; I will get the cheaper stuff for plinking.

Another question I have, why do people choose heavier grain bullet versus lighter one? Do the higher grain bullets have harder punch and lighter grain bullets have higher velocity? I am wonder exactly about the dynamics of the bullet grain, it never made complete sense to me, even though I read some things about it.

I suppose I will try to find some good match grade ammo while I can. Does anyone know what a good price to pay is for the Hornady .223 and .308 TAP match grade ammo?

 

[Kind of Blued]

Hornady TAP usually goes for about $1/round in .223, but it's good stuff. A heavier bullet simply retains energy better than a lighter bullet, which can translate into retained velocity (and potential) at long ranges, and penetration. Simply put, while a lighter grain bullet will start out faster, it will also slow down faster.

 

[mason_winston]

would it be correct to assume that rifles w/1:7 twist could appropriately handle 75 gr. bullets, then?

 

[Coronach]

Yes. 1:7 would be pretty much ideal for a 75gr bullet. Generally, the faster the twist, the better it will handle heavier bullets. 1:9 is a slower twist that is optimized for a mid-weight bullet, but it will often shoot 75gr OK, too. You'll have to try it and see.

Mike