help understanding ammo weight difference

[turbo2]

Ok need a little info help. I have only had pistols until now(just bought M&P 15 sport) and before I would just buy whatever ammo Wal-Mart had to go the range with. Now that I bought my AR I have been doing a k
little more reading. So here is my question, my AR uses 223/556 ammo has a 1/8 twist barrel,do I understand right that

1. the higher the weight the more accurate ie 70gr more accurate than 55gr
2. Shorter like indoor range I use a 55 and longer outdoor use something closer to a 70gr

thanks for any info to help clarify for me

 

[murphydog]

The theory is that .223/5.56 rifles with a faster (smaller second number in the ratio) twist barrel will stabilize heavier bullets better, but every rifle is different. Best to try a variety of ammo and see which works best for you and your particular gun. You may find it works best with 55, 62 or 70 grain ammo accuracy-wise.

 

[adluginb]

Has to do with the twist of the barrel. Yours is 1/8. Heavier bullets usually like the 70gr usually take a 1/7 twist (faster twist) to stabilize. Heavier bullets are more accurate at longer distances. A lot of AR's are 1/9 twist which are good for the 55gr bullets. You're in between and will probably shoot them the same. If your gun is marked .223 don't shoot 5.56 in it. If its marked 5.56 you can shoot 223 and 5.56 in it.

 

[turbo2]

thanks for the replies so far. So what makes the accuracy between manufacturers so different even if same weight and how do you decide which to get

 

[adluginb]

Closer tolerances in loading the ammo. Different bullet types of the same weight, different powder, etc. Pretty much all ammo is "minute of man". For range ammo I use the cheapest stuff available. Watch for sales on the good stuff in bulk. If looking for a precise 1 holer you need a bolt gun, not an AR. Not saying AR's aren't accurate but they tend to be more expensive for a more accurate one over a bolt gun.

 

[JohnnieB]

1. So what makes the accuracy between manufacturers so different even if same weight

2. and how do you decide which to get

1. If you ever find out, let the rest of us know.
Making the mystery even more interesting is that randomly selected cartridges from the same box of ammo will shoot differently in seemingly identical guns.

2. The simple truth is that some ammo shoots better in some guns and not as well in others. You have to try what is available and find out what your specific gun likes best. And what is best in your AR, or whatever, may or may not work well in your friend's AR, which is set up identical to yours.

 

[rburg]

Yes, there are differences in how they perform. But you've also got the Ford vs Chey, Coke vs Pepsi, Bud vs Miller problem. We often get questions on which 22 ammo is best for someone's gun. Don't trust anyone who gives you an answer. The only correct answer is to try all the candidates and figure it out for yourself. The ammo that's best in my gun might be awful in yours.

The real question is "do you need the very best?" An invariably, the answer will be no. Most of us can't out shoot our gun or our ammo. But we can outshoot the worst of the ammo in our guns. The methodology is pretty simple. Just go buy a box of all the candidate brands and bullet weights. Then go to the range, get serious, and shoot the best we can at each target. Then study the results. What you generally find is some ammo is significantly better with our guns and us doing the shooting. Some, and even fairly costly stuff doesn't work well at all for us. And sometimes you score a win. You discover one of the least costly shoots among the best. So you need to suddenly get smart and make an investment. Look at the box flap. Its got a lot number printed on it. Go to the place where you bought it and load up.

Then do something else that will be tough. Don't burn it all up. Keep a few boxes "put back". That's an old hillbilly term for save some. When you get to the point where all that's left is your stash, go buy another, single box of the same exact ammo. But be prepared for it to have a different lot number. And also be prepared for it to perform differently. If it does, you're back at square one, buying all the candidate ammo and looking for one thats up to your standards. Sometimes you'll even find a better one. But never burn up your stash, use it in the future to test other new lots.

For reloaders, its much more complicated. But then the results can be much more rewarding.

 

[WR Moore]

Little history lesson:

First, the comment that faster twist is needed to stabilize heavier, longer bullets is correct. Very light bullets with thin jackets intended for varmints may come apart enroute to the target when fired from your 1-8 twist, they also may not.

Second, the .223/5.56 round is available with bullets from 40 to 90 grains in weight. The heavier the bullet, the better the penetration. The real heavy weights, 70-90 grains, are generally target bullets intended for long range (400 yds +) shooting. The 40-60 grain bullets are generally lightly constructed bullets intended for small furry creatures. There are some bullets with extremely thin jackets that may cause the self destruction issues mentioned earlier, like the Sierra Blitz line. There are also match bullets around 52-53 grains in weight for benchrest shooting at 100-200 yards. Finally, there are several bullets between 60 and 70 grains (actually, 63 & 64 grain, from Sierra & Winchester respectively)designed for the taking of white tail deer, if legal in your state/province.

The common "ball rounds" featuring full metal jacket bullets from 55-62 gr in weight can pretty much be considered the same thing. The real question is what do you want to do with your rifle? If you're simply shooting casually, almost any ammo from 55 gr to 70 grains should stabilize in your weapon and group quite acceptably for most purposes. You may actually be able to use 75 gr loads, the 77 gr Sierra Match King would be iffy.

Individual rifles will have individual preferences in ammo. If you're trying to shoot itty-bitty groups, you'll have to experiment. Theoretically, your rifle should do a wee bit better with 62 grain, but it really depends upon how picky you're being.

 

[2hawk]

Good advice so far, I have several AR's and they are all a law unto themselves. One is a precision rig with a ss Krieger barrel, 1:7.7 twist- I've been able to manage a .363" 5 shot group at 100 yds with a scope, benched, using BH 68 gr blue box. It is a shooter! I would recommend the Black Hills ammo if you're looking for accuracy.

Here is a good source for info, maybe a little dated now, but still very comprehensive: :: Ammo Oracle

Good Shootin'

 

[nframes4me]

The longer the projectile is, the faster the rate of twist needs to be.
And the longer the projectile is relative to it's diameter the greater the weight will be for that caliber.

A 45 caliber roundball weighs 143 grains and needs a slow twist of one turn in 50 or 60 inches of barrels. A 45/70 rifle with a 400 grain bullet that is close to an inch long or more needs a faster twist rate of 1 turn in 20 inches.

Smith and wesson uses a 1 in 18 twist rate on their barrels for 357 mag, while Colt used 1 in 14 on their Python barrels when those guns were in full production. Both barrels stabilized the common 125 grain and 158 grain projectiles equally well.

Theoretically, the python barrel would work better with 200 grain bullets, but the fact is that twist rate appears to be less critical at pistol vbelocities than it does at rifle velocities.

As far as AR's I think you need to go to an AR forum and listen to all the many opinions specific to those guns and see what the general consensus is, but the basic principle still holds true, that the shorter, lighter-for-caliber 55 gain bullets work best wiuth a slower 1-in- 12 twist whele the longer heavier bullets need faster twists like 1-in-9, 1-8, and 1-7, and the longer and heavier the bullet, the faster the twist needs to be.