Please help me understand bullet "Weight"

[Kimio]

Forgive my ignorance, but when ya'll discuss bullet "weight" are you actually talking about the literal weight of the bullet itself or the powder behind the round?

Reason I'm asking is that I'm considering some time down the line of switching my 1:9 twist barrel of my AR15 to that of maybe a 1:7 twist to fire the "heavier" loads. As I understand it, "Heavier" rounds need a faster twist rate in order to stabilize them, "heavier" loads as I understand it are apparently more accurate as well when compared to the lighter bullets.

Some clarification would be appreciated.

[hodaka]

It is the weight of the bullet itself, typically measured in units of grains (like a pharmacy), not grams.

[Brian Pfleuger]

Weight could be the bullet or the charge but if they say "bullet weight" or "heavier bullet" for example, it's the bullet, not the powder charge.

Both the charge and the bullet are measured in the same unit though, grains.

[Marco Califo]

1:9 twist is very a good and very versatile, all around performer. In contrast, the typical bolt action Varmint rifles were usually 1:12 or 1:14. Today, if you want that slow of a twist from Savage, they have it in 22-250, but not 223, which are all 1:9 (or the single 1:7 linked below).

I shoot 223 75 gr Hornady HPBT with excellent long range accuracy, in a 1:9 Savage bolt rifle, while also doing fine down to 40 grn bullets.
Conversely, 1:7 twist may limit you to only shooting heavier bullets.

You will find a very good discussion of the twist rates here:
"only select a 1:7″ or faster twist barrel if we had a need to shoot the 90gr VLDs." http://www.accurateshooter.com/cartridge-guides/223rem/
You can also download both the Sierra bullets 223 guides (bolt and AR) there.

If I do buy a 1:7 223, it will be this one:
http://www.budsgunshop.com/catalog/p...ducts_id/60970
One reason is the 30" barrel length. Conversly, if you are shooting an AR you are only going to have 16-20" inches of barrel, and that will limit your powder choices, and velocity. Although you can get 24" heavy AR barrels, Bushmaster makes one (whole gun)..

[Doyle]

Kimio, let me see if I can make things a little clearer.

In any given caliber, the diameter of the bullet is fixed - carved in stone so to speak. So, to make one bullet that is heavier than another bullet there are only two ways to do it. First is to use a denser material (think using heavy gold in one bullet and light copper in another). Since actual bullets are generally made out of copper coated lead this option really isn't practical. The second option is to make one bullet longer than the other. This is the option that is actually used. With a caliber like .223, there is a HUGE range of available bullet weights. They are all .223 in diameter so the only way to make the range of weights is to make them shorter or longer.

If you have ever thrown a football, you'll know that you have to impart a spin to the ball in order to get any distance or accuracy. Bullets are just the same. A bullet that doesn't spin won't fly for crap. The amount of spin needed to make it fly "optimally" depends on the length of the bullet in relation to the diameter of the bullet. The longer a bullet is for a fixed diameter, the faster it needs to spin to make it fly right.

Continuing with our .223 example, spinning one revolution every 12 inches may be just fine for a short 40grn bullet. However, if you used that same rate of twist with a heavy 70 grn bullet it would be severely underspun and accuracy would be horrible. .223 rifle manufacturers will offer a fairly wide range of twist rates so that the user will be able to match the barrel up with the weight of bullet he intends to shoot. Conversely, knowing the twist rate of the barrel you already have helps you determine which bullet should shoot best out of it.

[Woody55]

In the context of your initial question, you are talking about the weight of the bullet (the projectile) itself.

In the beginning, the M16A1 fired a 55 grain bullet. If memory serves, the rifle had a 1:12 twist.

The A2 version fires a 62 grain bullet. To stableize the heavier bullet, the twist was tightened to !:7.

I have an AR 15 with a 1:9 twist. It does just fine with both 55 grain and 62 grain bullets. I've never shot a heavier bullet.

If you care, 1 pound = 7,000 grains. The only thing I use this for is powder for reloading. Like I put (slightly less than) 5 grains of powder in a .40 S&W cartridge case. That means the one pound container of powder I buy is good for 1,400 rounds.

[Sevens]

Great explanation! I just want to highlight this part for the OP:

The amount of spin needed to make it fly "optimally" depends on the length of the bullet in relation to the diameter of the bullet. The longer a bullet is for a fixed diameter, the faster it needs to spin to make it fly right.

So yes, we are talking about bullet weight and folks that pick different rifle barrel twists often believe they are picking their twist because of a bullet weight, but the truth is -- it's about the bullet length, not the weight. It just also happens that...the longer bullets weigh more.

Also, from the OP's initial question:

Forgive my ignorance, but when ya'll discuss bullet "weight" are you actually talking about the literal weight of the bullet itself or the powder behind the round?

When the average guy goes to the store to look at factory ammo, the only weight listed on the package is going to be the bullet weight in grains. As Woody55 nicely explained, "grains" is a unit of measure and does not mean "individual granules." It references a grain of wheat.

When you look at a box of factory ammo, the weight listed is that of the bullet, in grains. But when we look at handload data, either from ammo that we produced or from published data in a book, they list a bullet weight (in your AR, the weight being between 40 grains and 70 or so) and we also denote a powder charge weight -- which is also expressed in the grain unit of measure.

I tend to use around 19.6 grains of powder (H4198) under a 55 grain SP bullet in a .223 load that I like.

[brokenanew]

The 1:7 twist does not always mean it will shot those heavier bullets in an AR. especially VLD type of bullets or the AMAX. A lot plays into how well it will shot a heavier bullet including barrel length and whether its Heavy barrel or not.

Mine personally with a 1:7 twist wont shoot anything between 60 -77 worth a darn. But it will shoot half inch groups with the 77gr SMK and 3/4" groups with the 60 vmax all day long.

That aside, yes twist rate does have the most effect on whether you can stabilize a heavier bullet
1:9 should work well for anything 69 gr and down. Some people can get away with shooting the 75 gr well with a 1:9 but not likely with a shorter barrel like a mid-length (16") or under.

1:7 should theoretically shoot anything 69 gr or heavier well. Again there are more factors to consider. Some one made a good point its not so much the weight has it is the length with the exception of bullets with a good a non-sensative O-give like the SMK as opposed to ones that are O-give sensitive like the A-max (those are really long and wont stabilize well in my 16" 1:7). But its also the length that gives you the real distance. You have to sacrifice one or the other.

Look if its an AR the heaviest your going to be able to get WITHOUT doing single loading is the 77gr SMK. Even then it may not shoot worth a darn even when u play with the seating depth.

BEST thing to do is just try them and see. Good luck, sorry so long.

[UtopiaTexasG19]

"In any given caliber, the diameter of the bullet is fixed - carved in stone so to speak."

Well, Except in the lead cast bullet world. I hang out with a group of Winchester 30-30 fanatics that cast and reload their own bullets. In the group of 12 members we shoot .308,.309,.310,.311 and .312 diameter bullets depending on the weight and what is the most accurate in any particular rifle.

[TheDutchman19]

I have never quite understood barrel twist myself. Can some please clarify this for me?

1:7 = one rotation for every 7" of barrel?

[Doyle]

Well, Except in the lead cast bullet world. I hang out with a group of Winchester 30-30 fanatics that cast and reload their own bullets. In the group of 12 members we shoot .308,.309,.310,.311 and .312 diameter bullets depending on the weight and what is the most accurate in any particular rifle.

Yea, there are oddballs in every crowd.

[FlyFish]

I have never quite understood barrel twist myself. Can some please clarify this for me?

1:7 = one rotation for every 7" of barrel?

Yes, exactly. The smaller the second number, the more (faster) spin is imparted to the bullet (assuming a constant muzzle velocity), and faster spin will be better for stabilizing a heavier (really longer, as an earlier poster pointed out) bullet.

[Sport45]

Well, Except in the lead cast bullet world. I hang out with a group of Winchester 30-30 fanatics that cast and reload their own bullets. In the group of 12 members we shoot .308,.309,.310,.311 and .312 diameter bullets depending on the weight and what is the most accurate in any particular rifle.

Okay, for every firearm the diameter of the barrel is fixed. You can poke bigger bullets in it, but they won't come out any bigger than the bore diameter.

The A2 version fires a 62 grain bullet. To stableize the heavier bullet, the twist was tightened to !:7.

I don't think the 62 grain bullet by itself was long enough to merit the faster twist rate. Wasn't it the tracer that was too long for the 1:12? Tracer compound is quite light compared to lead.

[CrustyFN]

Reason I'm asking is that I'm considering some time down the line of switching my 1:9 twist barrel of my AR15 to that of maybe a 1:7 twist to fire the "heavier" loads. As I understand it, "Heavier" rounds need a faster twist rate in order to stabilize them, "heavier" loads as I understand it are apparently more accurate as well when compared to the lighter bullets.

Looks like you got a lot of great answers already so I would just like to add to be carefull with the heavier bullets. As someone posted already the heavier bullet has to be longer. When the longer bullets are loaded to the correct OAL then you are going to start out growing the magazine and you will have to load them one at a time. For me that wouldn't be much fun wuth an AR.

[UtopiaTexasG19]

"Okay, for every firearm the diameter of the barrel is fixed. You can poke bigger bullets in it, but they won't come out any bigger than the bore diameter. "

Well, not really. The reason a barrel is "slugged" is to find out the diameter of that particular barrel. One would think that a 1,000 barrels comming off the same assembly line would have the same exact diameter but it just isn't so. Also due to wear and tear, age and use, the diameters can range quite a bit.

[Sport45]

I think that's what I said. The bullets won't come out the end any larger than the diameter of the barrel.

I'm not disagreeing with you.

[Sevens]

Hey, if'n you guys wanna argue details, than CAST boolits can also vary in weight even if they are EXACTLY the same length and diameter and are complete dimensional copies of each other...

That has to do with the alloy make-up of the bullet.

[g.willikers]

And also the design.
A hollow point bullet will be a different length than a solid one, even if both weigh the same.

[wncchester]

we shoot .308,.309,.310,.311 and .312 diameter bullets

It's rare for a .30 cal. barrel groove size to be larger than maybe .3085" and all bullets will be groove size when they have traveled their own lenght.

[joneb]

I will add that the twist rate of the barrel and the velocity of the projectile determines the RPM of the projectile, longer bullets often heavier are leaving the barrel at a slower velocity and have less rpm's than the higher velocity lighter bullet.
Longer barrels have the ability of producing higher velocities and can stabilize longer bullets better than shorter barrels of the same twist rate, again its the correct rotational speed that stabilizes the bullet.
The military found that a bullet with a higher rotation speed or rpm had a greater wound effect on a soft target.

[UtopiaTexasG19]

Most of us use the "Ranch Dog" molds for our 30-30's and resize to .310 though I agree the lead cast will end up being what ever the smallest diameter is in the lenght of the barrel.

[FloridaVeteran]

To lighten things up a bit, 180 lbs. on a man is way different than 180 lbs on a woman. But you can't get a man to confirm that, only a woman.

[joneb]

To lighten things up a bit, 180 lbs. on a man is way different than 180 lbs on a woman. But you can't get a man to confirm that, only a woman.

Are you sayin these pants make my Butt look big

[elkslayer4x5]

Are you sayin these pants make my Butt look big

Ya know, I think he was......

[Marco Califo]

"Are you sayin these pants make my Butt look big"

No, no, no, . . . not at all.

(Fact is, I don't think the pants are to blame.)