Even'n shooters,
A PROPERLY (remember that word) reamed chamber, of any of the P.O Ackely "improved" cartridges is made to allow for the firing of factory or reloaded ammo of factory spects, to be safely and correctly fire formed in that chamber.
You do not need to fire form with less then factory pressure ammo!
30/06 in a 30/06 AI improved chamber, 243 Win. in a 243 AI improved chamber, 280 Rem. in a 280 AI improved chamber, 270 Win. in a 270 AI improved chamber, 257 in a 257 AI improved chamber etc.
That is one of the major differences between "wildcat" and "improved" chambers.
On wildcats, 30 Gibbs for example, you must start with a case of larger neck size, such as a 35 Whelan for this 30/06 based wildcat, ---- expand the neck of the 06 case to over size and then use the Gibbs die to size a false shoulder onto the expanded case neck - in the proper position, or do as follows.
By the way, Rocky Gibbs who lived and worked until the time of his death, resided about 45minutes from my home. So there have been lots of the different Gibbs rifles - all based on the 06 - in this area.
During my time with the 30 Gibbs, I would take 30/06 brass and long seat a bullet into the case.
By doing so, it forced the bullet into the lands and thereby held the head of the case firmly against the bolt face during firing - fire forming - and thereby prevented any head space issues during the first firing.
A proper type and amount of powder must be used during this process.
It is spoken of in writings about Rocky, of using factory ammo - without changing the bullet seating depth - to fire form brass to his 30 Gibbs cartridge. Seems risky to me, but guess they did it with some success.
The chamber on my 30 Gibbs was cut long. Meaning the gunsmith IMPROPERLY allowed the chamber reamer to ream deeper then he should have, creating a longer head to shoulder length then is normal.
The fire formed rounds filled out nicely, creating for me and even greater powder capacity then the normal 30 Gibbs, but at the price of a shorter the normal neck.
I have never had problems with "short neck" cartridges and had none with this incorrectly chambered Gibbs.
So, back to the "improved" cartridges.
Properly done, an improved chamber will have a VERY SLIGHT"crush fit" when a factory or factory spec. round is chambered. This will be between the bolt face and shoulder of the cartridge.
Any "improved" chamber which is cut deeper then this, has been too deeply and improperly reamed.
It can probably still be used, but steps must be taken during fire forming to prevent head space issues during the process.
AND, you take a risk when firing factory or factory spec. ammo in this "IMPROPERLY" cut improved chamber.
Keep em coming!
CDOC