Question on bullets and grains

F

Formynder

New member
So I know enough to know the best grain bullets for the various twist rates on my rifles, but I saw this today by Theohazard:

The 300 Blackout is basically a 30 caliber bullet in a 5.56 case. With 115 gr. supersonic loads you get very similar ballistics to a 7.62x39 or a .30-30, and with 220 gr. subsonics you get a super-quiet suppressed round that will still cycle the action and can still make good hits out to about 200 meters or so.

I thought that generally speaking, heavier bullets had more grains of gun powder in them and thus had more force and were generally faster. How is it that the subsonic load has nearly twice the grains of the supersonic load in this case? Is my understanding of bullets completely off?
 
Formynder said:
So I know enough to know the best grain bullets for the various twist rates on my rifles, but I saw this today by Theohazard:

The 300 Blackout is basically a 30 caliber bullet in a 5.56 case. With 115 gr. supersonic loads you get very similar ballistics to a 7.62x39 or a .30-30, and with 220 gr. subsonics you get a super-quiet suppressed round that will still cycle the action and can still make good hits out to about 200 meters or so.

I thought that generally speaking, heavier bullets had more grains of gun powder in them and thus had more force and were generally faster. How is it that the subsonic load has nearly twice the grains of the supersonic load in this case? Is my understanding of bullets completely off?
Click to expand...

Grain is not a measure of the powder in a cartridge, but the weight of the bullet. In Theohazard's example, the 115 grain bullet is much lighter, therfore faster, than the heavier 220 grain subsonic, therefore slower (all other factors being equal) bullet.

http://en.wikipedia.org/wiki/Grain_(unit)
 
The grains mentioned there are for the bullet itself, the projectile. Each cartridge is 4 parts:case, primer, powder and bullet. So when someone says a 220gr load or a 115gr load they're referring to the bullet. The amount of powder, also weighed in grains, would fall into a much lower and smaller range. Without digging out a manual, I'd guess in the ball park of 40grs +- a few grains of powder would be the entire safe range for all the .300blk loadings from 115 to 220gr bullets.

eta:jimmy beat me to it!
 
I thought that generally speaking, heavier bullets had more grains of gun powder in them and thus had more force and were generally faster. How is it that the subsonic load has nearly twice the grains of the supersonic load in this case? Is my understanding of bullets completely off?
Click to expand...


Both the powder charge and the bullet weights are measured in grains.
In this sentence you have chosen they are talking about bullet weight not powder charge.

You can load a case with less powder to get less speed and less energy, but typically cases are loaded near to max so you can't really put more powder in to make it shoot faster. And obviously the heavier bullet you put on the slower it will go with the same amount of powder.
The only way you can get a heavier projectile to go the same speed or faster, is to start with an under powdered load to begin with, or you have to get a larger case.
Eg step up from a 223 to a 22-250 and have a 75gr bullet going the same speed as a 55gr in a 223.
 
Without digging out a manual, I'd guess in the ball park of 40grs +- a few grains of powder would be the entire safe range for all the .300blk loadings from 115 to 220gr bulle
Click to expand...
I don't know about .300 AAC, specifically. But the .223/5.56 case, in general, uses powder charges of around 19 to 28 grains (depending on the powder). In the .300 AAC, I'd expect powder charges to be in the 14 to 20 gr range.
 
For grins I pulled up Hodgdon's data center for the .300BLK. Interesting info, I hadn't checked load data for that cartridge.

Looks like the supersonic loads do indeed tend to run in the 14-20gr range for most rifle powders (there's a weird 4gr Trail Boss load for some of the lighter weight ones), but the heavier bullet subsonic loads tend to run much lower charges of pistol powders (H110, Lil'Gun) in the 8-11 grain range.


Generally, though, the heavier the bullet for a given caliber the slower it will go. The heavier and slower bullet will hit nice and hard at shorter ranges but be more susceptible to bullet drop as range increases. The faster one will have a flatter trajectory but the lighter weight means it won't do quite as much to the target.
 
Thanks y'all! I always just assumed that since it said grains it just HAD to be talking about grains of powder.
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one of the biggest points of confusion for people just getting into shooting is the use of "grain" weight.

"Grain" weight as used in the weight of bullets and powder comes from the Avoirdupois system of measure, the one in common use in the US. Grain weight was and is used for small amounts of weight, and sometimes is called the Apothecary system, because it was commonly used by chemists and druggists.

1 pound = 7000 grains
1 ounce = 437.5grains

The confusion with powder comes from the most common word to describe the individual powder kernels, the word "grain". When we say a 40gr powder charge, we are talking about 40 grain weight of powder, NOT 40 individual kernels of powder, be they flakes, sticks, or little spheres.

Hope this helps
 
Another possible point of confusion:

formynder said:
So I know enough to know the best grain bullets for the various twist rates on my rifles, but I saw this today by Theohazard:
Click to expand...
It's possible that it's MY understanding that is faulty, but I believe the twist rate for optimal stabilization is a function of bullet length rather than bullet weight. Certainly, with a given caliber there is a relationship between length and weight, but what I've read (particularly in regard to the development and maturation of the AR-15 and cartridges for same) suggests that the twist rate is really optimized for bullet length.
 
6? or half a dozen?

..suggests that the twist rate is really optimized for bullet length.
Click to expand...

Well, yes. And no. Or at least, not entirely. Because the bore diameter is a fixed dimension, a heavier bullet must be longer, because it cannot be wider.

Its not exactly that they are heavier because they are longer, its more they are longer because they are heavier.

Look at the match bullets in "standard" weights, they are longer than regular hunting bullets (SP) and often are longer than FMJ of the same weight. Not a lot longer, but a little. This is because of the jacket design, placing the bulk of the core weight towards the back end of the bullet. They are a hollow tip design, but not a hollow point intended for expansion.

And they shoot very well with the twist rate for the shorter "standard" bullets.

When you increase the weight, the bullet gets longer, and the distribution of the weight (center of gravity) changes. This is what makes a different twist rate necessary.
 
The things we are talking about here are very enlightening to many folks who have never handloaded -- most are the very basic foundations of handloading. These things (and many other things!) become very apparent when you learn to roll your own ammo. It's an extremely rewarding hobby that goes far beyond simply being able to "get your ammo cheaper." (which isn't always the case, by the way)

Most of the best info has already been offered, but here's another nugget that might help:

It was mentioned above that when factory ammo is advertised or shown on the packaged with a "grain", they are always talking about the weight of the projectile. This is always going to be true, and always has been in any factory ammo I've ever seen. But there's another little bit to that to help understand WHY they are always talking about the bullet weight and never about the powder charge.

Quite simply, the big ammo manufacturers (Win, CCI, Federal, R-P, Hornady, etc) use extremely large lots of powder when they craft their products, and that powder varies from lot to lot as a normal byproduct of it's manufacture.

So while handloaders will sit down with a one-pound plastic container of powder and craft a loaded round by specifically weighing out a single charge of powder at a known weight... the big ammo manufacturers do NOT do that.

Instead, they use their extensive and comprehensive labs & equipment to pressure test their loads. When they serve a big load of powder, they craft the loaded cartridge around a pressure goal and not a specific recipe by weight. The actual weight of powder should be the same across that entire production run, but it may not be the same as an earlier production run.

If you went to a gun store and bought 5 boxes of CCI Blazer Brass and yanked all the bullets out and weighed each powder charge, you should find a very similar weight across every single one of those rounds. However, if you compared that powder charge to a box of CCI Blazer that you purchased two years ago, there's a -VERY GOOD- chance the powder charge weight would be different.
 
Doc TH said:
"a 30 caliber bullet in a 5.56 case.."??

How do you get a .30 cal. bullet into a 5.56 mm (.223") case?
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Assuming he is referring to a .223 Remington/5.56x45 case, the case is necked down to accept the .223 projectile. The case itself is easily large enough to accept a .30 caliber bullet.

http://www.saami.org/PubResources/CC_Drawings/Rifle/223 Remington.pdf

The case diameter near the head is .3759", and farther forward, but before the neck, it tapers to .3542".
 
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