Explain something to me

[44 AMP]

In your 45 caliber
pistol cartridge, the limiting factor is pressure. A heavier projectile creates more resistance, driving up pressure. To keep the pressure in the safe and sane category a reduction of propellant is required

Consider looking at it this way...

Pressure limit is the constant (for all cartridges). You can use UP TO "X" amount of pressure, but no more.

Bullet weight is what you are pushing with that pressure. In the same bore size, since the pressure is a fixed max, the lighter bullet goes faster.

While the heavier bullet has greater resistance to moving, it does not create more pressure. Pressure is created only by the powder charge burning, and the amount is dependent on the amount/type of powder and the area available for it to burn in.

Heavier bullets do require a reduction in powder charge compared to light bullet loads, for two main reasons, one being they are "harder to move", and the other being, generally, they take up more space in the case, changing the available volume.

So, a reduction in powder charge depends on your point of view and where you choose as your standard. Take the .45acp and the 230gr ball, vs a 200gr swc or hp. IF the powder charge for those is you standard, then yes, the 230 requires a reduction. But if the 230 is you chosen standard, then the lighter bullets ALLOW an increase. They don't require it, you can shoot them with the same powder charge you use for the 230, and they will go faster than the 230, as they are lighter, but being lighter allows an increase in powder charge within the same pressure limits.

 

[Unclenick]

Heavier bullets do require a reduction in powder charge compared to light bullet loads,

Needs the caveat if the caliber is the same. What has thrown a monkey wrench into this thread is the OP is comparing two different bullet diameters.

 

[74A95]

So, a reduction in powder charge depends on your point of view and where you choose as your standard. Take the .45acp and the 230gr ball, vs a 200gr swc or hp. IF the powder charge for those is you standard, then yes, the 230 requires a reduction. But if the 230 is you chosen standard, then the lighter bullets ALLOW an increase. They don't require it, you can shoot them with the same powder charge you use for the 230, and they will go faster than the 230, as they are lighter, but being lighter allows an increase in powder charge within the same pressure limits.

Real world data does not support your statement. In fact, just the opposite. The lighter bullets generally go slower when powered by the same powder charge. See Table 2 here:

https://www.shootingtimes.com/editorial/power-factor-recoil-bullet-weight-gives-edge/99399

 

[RC20]

Something I have been pondering is the new 6.8 mm Cartridge Sig makes for the US Army.

Now my Savage rifles all have 1 inch barrels but when I hit the pressure limits I get hard bolt lift, case wipe and usually primer change.

So what allows that 6.8 to shoot at such high pressure with the same barrel base? My guess is different metal but rifle use both stainless and steel and the chamber size is the same at least up to the magnums and even then my Savages only go a slight larger size.

 

[44 AMP]

Real world data does not support your statement. In fact, just the opposite.

You're going to have to show me, here. The link you provided had no tables, and barely mentioned velocities and was primarily concerned about making a given power factor and recoil. There were web adresses, but did not function as links for me, and I'm not chasing down those particular rabbit holes, sorry,

I think, perhaps, you misunderstood my meaning.

When dealing with the same caliber, case and powder charge, how can a lighter bullet NOT go faster than a heavier one? You'll have to show me actual proof., that disproves what my loading manuals say.

For just one example, my Lyman manual lists the same (max) powder charge of Unique (7.2gr) for both the 230gr jacketed and the 200gr cast slugs in .45acp. same test gun, same load, same components, same everything except the bullet. 230gr clocked 960fps, the 200gr went 1041 from their test gun.

I realize its old data (1970) but I'm an old guy and I find it difficult to believe what was true then is not true now. So, you'll have to show me.

DO understand my point was not about what it takes to drive the lighter bullet to reach a desired energy level or recoil level or anything else, all I was saying that IF you shoot a lighter bullet over the same powder charge used for a heavier bullet the lighter bullet will go faster than the heavier bullet does.

It might not be (and probably isn't) the speed you are desiring, but it will be some amount faster than the heavier slug when pushed by the exact same powder charge.

 

[74A95]

Try a different browser. It did not show figures/tables in Chrome, but it did in Firefox.

I was saying that IF you shoot a lighter bullet over the same powder charge used for a heavier bullet the lighter bullet will go faster than the heavier bullet does.

The table 2 shows the opposite result.

 

[74A95]

Hey, I got it to work!

Figure is from: https://www.shootingtimes.com/editorial/power-factor-recoil-bullet-weight-gives-edge/99399

 

[44 AMP]

Alright, thank you. I don't understand why that table goes against decades of information I have, so there is clearly something about how they got that data I do not understand.

I looked through Lyman, Hornady, Speer and other reloading books and a dozen or so different cartridges in each, and all had the same pattern, which is 100% the opposite of that shooting times table you were kind enough to show me.

Where the difference in bullet weight was very small (like 50 vs 55gr in .22 cal) using identical charge weights of powder the velocity was essentially the same. Where the difference was a larger percentage (say 40 vs 55gr), the lighter bullet was faster, though I did find a couple of examples where the bullet weight difference was 20% and delivered the same velocity. I looked at rifle and pistol rounds ranging from .22 to .45 caliber and in no case was the lighter bullet ever slower than than the heavier one, over the same charge of powder.

Might you have any idea why that table showed the exact opposite of over 50 years worth of printed data from numerous independent sources??

I have seen many strange things happen with guns and ammo velocities, unexpected differences and even complete overturning the established norms, but every one of those has been the result of something unique to the firearm or ammo being tested, and not something generally applicable overall.

For example, I've seen a 4 inch revolver turn in a higher speed (barely, 15fps than an 8 inch firing the same ammo, but that was the result of a particularly "fast" barrel in the 4 inch and a spectacularly slow one in the 8 in gun.

I've seen different guns with "identical" barrel lengths turn in as much as 100fps difference shooting the same ammo. Not common, but I've seen it.

I'm not disputing what they got, but absent a lot more information, I cannot understand how it happened, and I do not consider it applicable in general.

Ok, I guess I could look at it as "the exception proves the rule" but IF, generally speaking a lighter bullet moves slower than a heavier one, over exactly the same type and amount of powder, why is this not common knowledge and widely known?

Thank you for the table showing the data, but I remain unconvinced it is a general result, and not a unique "one time" thing.

 

[74A95]

It might be an exception to the rule. I don't know. But you're right, when I look through manuals it shows the lighter bullet going faster or as fast as the heavier one with the same powder charge, at least for the stuff I looked at. Chalk it up to 'life is full of mysteries'.

 

[Unclenick]

I suspect it has to do with the powder choice, with slower powder needing more inertial resistance from the bullet to provide enough confinement to light up promptly and burn thoroughly. Folks playing with very light-for-caliber bullets or with light bullets in sabots find these bullets can scoot down the barrel so fast the powders they usually use can't maintain their burn well, so they wind up with disappointing muzzle energies and a lot of unburned powder on the ground in front of them. Going to faster powders corrects for that.