Do bottleneck cartridges increase pressure?

[dgang]

Wanted to ask a question that puzzles me. Do bottleneck cartridges increase pressure? I can load 22gr. of H110 under a a110gr. bullet and achieve about 35,000 PSI. However, if I load 22gr. of H322 in a .223 case under a 69gr. bullet I'm loading about 55,000 PSI. Why does a smaller case (.357) with a much faster powder and a heavier bullet result in less pressure? I was told that a bottleneck cartridge does not increase pressure. What goes?
Thanks in advance and good shooting' to ya, Dgang

 

[Blue68f100]

It's the amount of gasses the powder produces when it burns in relation to the volume. That is why there is over 100 powders to chose from. Most were developed for a particular round.

 

[Texas10mm]

It's the amount of gas produced and the rate at which it's produced, also if it has nitroglycerin added.

 

[Bfh_auto]

You also have the expansion ratio of the case to bore diameter to take into account.

 

[Walkalong]

Try blowing through a straw, then try to blow one through a two diameter straw.

 

[tightgroup tiger]

Look at the size of the base of both bullets and imagine the square inches of surface area. The larger bullet has more surface area on it's base so it will take less pressure to move it than a smaller bullet will of the same weight. If you increase the surface area of the piston (bullet) it will take less pressure to do the same amount of work as a smaller piston takes because there are more square inches of the same pressure pushing on it.
Even though you listed two different powders with different burn rates, I'm keeping this as simple as possible for what I think your asking about.

 

[dgang]

Hey tightgroup tiger,

Look at the size of the base of both bullets and imagine the square inches of surface area. The larger bullet has more surface area on it's base so it will take less pressure to move it than a smaller bullet will of the same weight. If you increase the surface area of the piston (bullet) it will take less pressure to do the same amount of work as a smaller piston takes because there are more square inches of the same pressure pushing on it.

Yeah, that about what I'm thinking about. So, in effect, the .223 brass being necked down to .224 DOES increase the pressure more than if the cartridge was NOT necked down and the projectile was the same size as the case.

 

[Dudedog]

Well yes sort of but no, if the cartridge was not necked down you would have a bigger bore, more room for the gas to expand.
Burn some powder, if there is nothing to prevent its expansion pressure drops to atmospheric quickly, not much happens other than heat generated.
Burn the same powder in a closed/semi closed vessel, pressure generated depends on how much/fast the powder can expand. (BTW to much pressure for the container = kaboom)
Volume of a cylinder is V=pi r(squared) h
So say a .224 dia barrel 16" 3.14159*.224*.224*16 = 2.2551
.30 dia barrel 16" 3.14159*.30*.30*16 = 4.52
.35 dia barrel 16" 3.14159*.35*.35*16 = 6.157 (close to 2.5 times as much volume as the .22 barrel)
More space for the gas to expand in a larger dia barrel=less pressure


Boyle's law - Wikipedia
The law itself can be stated as follows: For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional. Or Boyle's law is a gas law, stating that the pressure and volume of a gas have an inverse relationship, when temperature is held constant.

I would guess pressure would be close if you burned the same amount of powder in say a .223 case and an imaginary really long straight wall .22 case of the same volume.
Simply the bottleneck case exists so you have more space for powder while keeping the case length reasonable.

I am ignoring lots of things in the above example but just attempting to try to "paint" a quick picture