This seems backwards

Howa 9700 said:

So getting ready to put together some test loads in 243 Win.

Powder I'm going to use is IMR 4350. Bullets are 85 grain and 100 grain. From Lyman 50th, starting powder charge for the 85 grain bullet is 38 grains powder, max is 44.

Then for the 100 grain bullets, starting powder charge goes DOWN? Starting at 35.5 to max of 39.5.

So bullet weight goes up and powder charge goes down?

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Yes because otherwise, you'd generate too much pressure in the chamber

Its pressure. The heavy bullet causes more resistance and creates more pressure with the same powder charge.

All things being equal... 50grn of SuperDuper powder, first behind a 50grn bullet, then a 100grn bullet... the 100grn bullet load will produce higher pressures due to the higher bullet weight (and other factors.)

The heavier bullet is harder to move. More pressure builds quicker.

Howa 9700 said:

Another thing I find whacky, at least to understand, is the different powders used in 243 Win, 260 Rem and 308 Win. All use the same parent case of 308 win. The 308 Win is loaded with a bit quicker powders like 4064 or Varget and smaller diameter bullets like 243 use slower powders like 4350 or 4831. From a distance it would seem all three cases would use the same powder.

Which I guess is why you don't try this at home. Follow the manuals.

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I had to seriously study the reloading manuals and follow along with some threads to fully understand burn rate and other factors for any given cartridge. The 6.5CM was one in particular.

The 100 grain bullet is longer than the 85 grain bullet. There is more space in the case with the 85 grain bullet than there is for the 100 grain bullet. Also since the longer bullet is heavier the pressure inside the case would be more if you used the data for the 85 grainer. Check the picture out.

Howa 9700 said:

unless pressure is acting on surface area and the larger diameter bullet makes for a bigger escape valve?

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^This... Kinda

Yes, the pressure has a larger surface area to push the larger diameter bullet. True. This also means, that as the bullet travels down the barrel, the volume of gas needed to fill the larger bore diameter of the barrel is greater. Therefore, you need a powder that can generate a larger volume of pressurized gas fast enough to push that bullet down the length of the barrel.

On the other hand, with a smaller diameter bullet (for this example, going at the same FPS), you need a smaller volume of gas in the same amount of time. Hence, the slower powder.

I recommend that you reference more than one reloading manual just to be sure information is similar or corroborated from another source.

I used to use the Lee manual solely for all of my reloading then I discovered that some of the info was a bit off when I started loading 38-55 cartridges. A friend recommended the Lyman manual so I bought it and found that Lee's info, while safe, was limited. Since then I have acquired several manuals and I balance information between them depending on what cartridges I am hand loading.

Howa 9700 said:

I had noticed the pressure rises in the data. Less powder, yet pressure goes up when bullet weight goes up.

That would then suggest that if you can live with the lower velocities, if you were trying to ration powder in short supply, you will get more loads per pound of powder using the heavier bullets?

The factor related to that would seem to be that a heavier bullet will deliver more foot pounds of energy to the target. Not sure who wins that contest. Lighter, faster bullet or slightly slower, heavier bullet.

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it depends on what you want that bullet to do.

Velocity isn’t everything, I used to think it was.

Throw a ping pong ball and see how far it goes, now throw a golf ball.

Way more technical but you get the idea. That 65 grain bullets in your .243 puts outs some impressive velocity. But if you want a bullet to carry at long distance you should probably look at something like the Berger 105 grains bullet, if your barrel will stabilize it. The velocity of the 105 isn’t that impressive, but the drop will be less at 500 yards and beyond.

I shoot somewhere in the middle bullets in most calibers, but premium constructed bullets since I like penetration.

For me personally, the priorities are:

1) Accuracy
2) Penetration
3) BC
4) Velocity (distant 4th)

Same diameter with a lighter bullet gives you more case volume and less pressure required to push the bullet.

Heavier bullet takes up more volume in the case and requires more pressure/force to move the bullet due to weight of the projectile and bearing surface friction.

It’s not the powder. It’s the weight of bullet that increases pressure. You can use less powder and increase pressure.

Check your manual, any manual, and see if there’s a heavier bullet that can travel faster than the same diameter lighter bullet at a max charge of the same powder….There isn’t one.

kalielkslayer said:

Velocity isn’t everything

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That’s a fact. You can push a bullet as fast as it’s construction will allow. But if the end result is piss poor accuracy, you’ve gained nothing and are wasting powder.

I think the ONLY cartridge I use a max charge on is my 10mm with BlueDot. And I load a lot of different cartridges.

Howa 9700 said:

Not sure who wins that contest. Lighter, faster bullet or slightly slower, heavier bullet.

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I'm not sure how long you've been into guns and shooting, but I wouldn't hold my breath while waiting for someone to "win" that contest. I've been listening to, and reading about "light and fast" vs "slightly slower, heavier" bullets my whole life (I'm 73), and I haven't seen a clear winner yet.

Howa 9700 said:

That would then suggest that if you can live with the lower velocities, if you were trying to ration powder in short supply, you will get more loads per pound of powder using the heavier bullets?

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Self evidently.

Howa 9700 said:

Not sure who wins that contest. Lighter, faster bullet or slightly slower, heavier bullet.

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Welcome to the argument were been enjoying ever since the second Chinaman built the second blackpowder cannon.

While we may not use it ourselves since we have the end data, there is all sorts of physical science, engineering formulas and geometric calculations involved with creating safe loads for publication.

We get to test how all that work others have done for us performs on paper (or on critters) when we follow the recipe and shoot it in our firearms

Stay safe.

I was always taught to verify a recipe from 3 sources. If you go Hodgdon/IMR POWDER LOADING web-site, you will find you can use those powders WITH IN LIMITS.
.308 is limited to a 110 grain bullet on that site. So you won't find the same recipe or possible powder as you can for your 100 grain bullet. So in .308 you have to get up to 130 grain bullet to use Varget for example.
But you can shoot all those powders if you want. Lyman must think some powders are better for your caliber than others and they have limited printing space for all possible combinations. You have limitations too, IMR-4350 and H-4350 are not the same, so don't confuse them. Also, H-4831 is not the same as IMR-4831 so be carefull and double check you charges, powder type and bullet size. You CANNOT LOAD H-4831 with a 85 grain bullet, but you can with a 100 grain bullet

Not just the weight of the bullet but geometry also affects pressure.

A 30 cal 180 Sierra matchking makes more pressure than a 185g Berger VLD with the same powder type and charge because the SMK has more bearing surface

Heavier bullets are longer. So when you seat them with the same overall length as the lighter bullet it creates a smaller space for the powder. Since the space is smaller it does not take as much powder to create the same amount of pressure.

Howa 9700 said:

Will tack this on here vs. starting a new thread. Last powder I bought (long time back) was in the metal cans. New stuff we just picked up is in the new plastic containers. In this case, 1 pound of IMR-4350. Was a little surprised to see the bottle was not sealed up beyond the screw on lid? Was it supposed to be? I would have expected one of those tamper proof films like you see on most foods.....more to keep it sealed up from the elements than safety....but sealed just the same.

If no, and that is normal, then no worries. If yes, then I'd have to start backtracking on the source. Was purchased from a retail shop that peddles reloading supplies.

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That’s pretty common. If there was a seal, it comes off with the lid most of the time.

I’m not a physicist, and I’ve never played one on TV, but as Boyle’s law states, “pressure is inversely proportional to volume given the mass of the gas is constant”

I think (and it’s just an opinion) that the principal volume at play here is in the barrel. Larger bore diameter, larger volume. For example, keep going past the .308 and look at the .358 win. Roughly the same case capacity as the .308 (minus the neck) running bullets from 200g up to 250g. It uses powders on the faster side and it uses a lot more of it than the .308.

A typical .358 win load for a 225g load would be 48g of H4895 (I’ve also used Benchmark and VV N135). Try 48g of any of those powders with a 200g 30 cal bullet and you’ll be beating you bolt open with a mallet, if you’re lucky

Hartkopf said:

That’s pretty common. If there was a seal, it comes off with the lid most of the time.

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I agree. Happens to me just like this all the time. It also threw me off at first too.

For what it's worth, VV powder containers have a great seal on them. Perhaps they should considering the premium price.