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

The capacity of the case relative to the size of the bore makes quite a difference. For example, the 243 Win. and 358 Win. are both based on the same 308 Win. case, but they need different powders.

Yes exactly. Case capacity vs bore size is your first step to understanding the necessary burn rate. Peak pressure plays a part in that as well. Case shape really has very little to do with it.

To go a step further with it...the volume behind the bullet changes as the bullet moves down the bore, and the larger the diameter of the bore and bullet, the faster the volume behind the bullet increases. In that case the powder needs to be transforming to a gas at a faster clip to maintain pressure (which is needed to get the velocity we love so much), so we use a faster burning powder.

Conversely, with a smaller diameter bore and bullet, we don't want the powder to burn too quickly. The bullet's movement provides pressure relief and if the powder is generating gas too quickly for the acceleration of the bullet to relieve pressure, bad things happen.