If you want a lesson in breech thrust shoot the standard .25-35 in the Thompson Center Carbine. My 24” carbine had difficulty extracting cases when using low pressure, published load data.
Switching to the .25-35 Ackley Improved case changed the rifle completely.
The TC 24” barrel chambered for the .25-35AI case will easily push various 100 grain bullets above 2,900 fps using several powders. I have pushed the 100 grain bulk Remington bullets to just over 3,000 fps using Alliant Reloder 15 but that is obviously more pressure than is prudent.
The 117 grain bullet is easily pushed above 2,800 fps. I have pushed the 117 grain Sierra Pro Hunter above 2,900 fps – again using Reloder 15 – but this is pushing things.
I have never experienced sticky extraction using the .25-35AI cartridge case.
I have loaded the .30-30 Ackley Improved quite a bit in both Marlin and Winchester lever action rifles. The .30-30AI can be loaded to high pressure in the lever action rifle.
If you need examples of the actual value of the Improved case shape these two cartridges will deliver.

Few of us have the opportunity to read a lot of PO’s writing as he wrote mainly for periodicals and the details of much of his experience are buried with little ability to found.
An easily found little article defining the Improved cartridge is this one:

Wildcat and Improved Cartridges
P O Ackley
Lyman Reloading Handbook 42nd Edition

The purpose of the improved idea is to create more powerful, longer range cartridges than their commercial counterparts by the more simple method of fireforming. Other reasons are to produce a cartridge of more modern design intended to eliminate certain annoying characteristics of some factory versions. Most improved designs take the form of minimum body taper combined with sharp shoulders. This general design results in reduced bolt thrust, reduces stretching or forward flow of brass and increases the case capacity. Any cartridge which is not already over bore capacity can be fire formed to some improved design, thus producing a case of better design and greater powder capacity which in turn makes it possible to hand-load to higher velocity. With factory cartridges with a volume too great for the bore, fireforming can result in little or no increase in velocity.

Often times, claims made for many wildcat and improved cartridges should be closely scrutinized by budding wildcatters. Certainly some small change in an existing cartridge is not going to revolutionize the business. Often velocities are quoted which have been obtained in an individual rifle which for some reason will accept loads which might reduce the average rifle of similar caliber to a pile of junk.

H P White Laboratory wrote a hit piece on PO’s .30-06 Improved case in the December 1953 American Rifleman – How Improved Is It? PO answered his critics in the October 1954 edition of the American Rifleman

Improved Cartridges
P O Ackley
American Rifleman October 1954

The word 'improved' is an unfortunate choice, and just grew up in connection with certain developments which were made with several objectives. One consideration is increased velocity. Another is mechanical improvement, which results in minimizing certain faults of standard cartridges.

My All Time Favorite Ackley Quote:
At the beginning of these comments certain things were pointed out as possible improvements, but nothing was said concerning pressure. Whether the handloader or wildcat enthusiast is right or wrong, he is interested in several things, most important of which are increased velocity and whether the bolt stays in the gun. If he can achieve these two results without serious complications, he is not overly concerned with the actual pressure readings in pounds per square inch.

Here is a picture of PO’s pressure and bolt thrust gun from the article Wildcat Pressures, Handloader 5/6 1966.
[Linked Image]

Slim