Curiosity on bullet weights and powder levels

[Mikhail2400]

Im very new to reloading, im about a year into it now and im going to ask a question which may make me look dumb. I can live with looking dumb.
I was looking up some .40S&W data and I noticed a trend that ive seen before. (Ill just give bullet then powder weights)
180g 4.6g
165g 5.2g
135g 6.7g
Now one would think the heavier the weight of the bullet the more powder needed to move it but thats not how it is. Ive thought about this a bit and the only thing I came up with was; The heavier the bullet the harder it is to move it and the slower it moves up the barrel which allows the powder burning to build up more pressure.
So is that why the recommended powder levels are pretty much always higher for the lighter bullet? Or am I a dumbazz who has this stuff completely wrong?

 

[Jeff Porter]

Those heavier bullets are harder to move. The inertia of the bullet causes pressure to build up in the case and chamber such that heavier bullets reach max safe pressures with less powder. Lighter bullets will give less resistance to movement and more powder can be burned before the pressure raises to unsafe levels.

 

[Gargoyle]

You're thinking correctly.

 

[Mikhail2400]

Those heavier bullets are harder to move. The inertia of the bullet causes pressure to build up in the case and chamber such that heavier bullets reach max safe pressures with less powder. Lighter bullets will give less resistance to movement and more powder can be burned before the pressure raises to unsafe levels.

You said it much better than I did.
Thanks for the replys folks and im very glad to see that im starting to get a much better understanding of reloading

 

[NZ_Fclass]

Nice to see another new reloader a) thinking and b) asking questions. There is so much expertise on this forum - and no-one belittles the new guy. We are all here to help and encourage people into our sport.

In answer to your hypothesis, it's even more evident in rifle cartridges. At times a slower powder can be used for heavier bullets to alter the pressure curve, rather than a much reduced load.

 

[RegionRat]

You said it much better than I did.
Thanks for the replys folks and im very glad to see that im starting to get a much better understanding of reloading

TL;DR - If you are going to do load development in an environment where things are hard to find and you are forced to use what you got, you can learn a lot from playing with an internal ballistics simulation program.

The guy that created the Gordon's Reloading Tool (GRT) internal ballistics program, passed away very recently.

While his program is still online and available, I mention he passed away so that you don't procrastinate.

Hard to say if his partners will keep that alive or if it will evaporate. (I hope his wife and loved ones will carry on and his legacy survives.)

For fun, all you need to do is create a free account and download the program. It costs nothing.

The software is portable and won't take long to learn. You can then play with bullets, powders, recipes, etc., and try to get a feel for the pressure and velocity by playing with your selections.

In what they call the compact screen, you will find that common calibers, bullets, and powders will come straight from the database and you won't have to go searching for dimensions or data. You can just learn the ropes by playing with default values for things while you learn.

Internal ballistics takes a while to digest. Since some folks won't have the background in engineering, thermodynamics, chemistry, calculus, programming, etc., the alternative is to use a program like GRT to develop a feel for internal ballistics by just playing with drop down menus and changing charges, barrel lengths, seating depths, etc.

Down the road, you may even find the program useful for planning which bullets or powders to test.

 

[DHall_37]

There is something I learned in physics last year that might help.

In order to get an object moving from rest, for example: moving a piece of wood on some coarse sand paper.

It will take more energy to get it started moving than once its moving, as it’s moving along the force required to keep it moving at a constant speed reduces.

the same can be applied to ammunition, pressure will spike when the bullet leaves the case and hits the lands. The heavier it is the more energy it takes to move, but gunpowder isn’t a constant pressure, it increases over time in a contained environment till it hits its peak.

more powder and a slow moving heavy bullet will spike pressures. Less powder is required to keep a heavier bullet at safe operating pressures.

This is probably explained poorly, but I’m only 18 and trying my best! I’m a new reloader too.

 

[3Sigma]

Another point regarding semiautomatic pistol rounds...

You load to a consistent overall length, regardless of bullet weight. Bigger bullets = longer bullets = more bullet in the case = less powder volume.

Pressure increases with less initial combustion volume. Combined with a heavier bullet and you need to reduce powder mass to maintain pressure.

 

[K22]

There are no dumb questions - don't be reluctant to ask questions on this site if you have them. That's part of what this site if for, to help fellow shooters, especially beginners.

Best wishes

 

[D-4297]

Another point regarding semiautomatic pistol rounds...

You load to a consistent overall length, regardless of bullet weight. Bigger bullets = longer bullets = more bullet in the case = less powder volume.

Pressure increases with less initial combustion volume. Combined with a heavier bullet and you need to reduce powder mass to maintain pressure.

And that is exactly the reason I load my 185gr. , 40cal loads at 1.145" instead of 1.125". I use a slightly larger powder load than standard , and by loading "Long" , it helps to smooth the pressure spike , while adding Velocity . Adding distance accuracy , and "Hit Power", at the other end . Do not try this at home without proper supervision !

 

[6MMsteve]

you are now entering the Wabbit hole, keep your earplugs in. bullet type & make by bearing surface is a good example for pondering I think