Sparks134:
The cartridge overall length to start with should match what is in your reloading manual for the exact bullet you are using. It is not effected buy the shorter case overall length. You really should be using the reloading manual as sold by the company whose bullets you are using. Sometimes the bullets effect the friction in the barrel and consequently the pressures there too. The manufacturer of the bullets test for that and his data will be safe in any SAMMI conforming gun whose standardizing cartridge and chamber specs most all manufacturers strive to achieve.
As part of load development you may want to change the overall length to set up the freebore for the bullet before it enters the rifling. But be aware that as the case capacity is reduced from the manual number, the pressure goes up as it does when you position the bullet out to almost touching the rifling. So when you change the bullet seating like this you really can not be anywhere close to the listed max powder load and you are much safer at the staring load level. and working up the load level, watching for signs of excessive pressure.
LDBennett
The COAL listed in the manual is merely a guideline and is NOT a recommendation or a requirement. Some manuals do not even list COAL as it is that un-important. Barnes for example, says .050 off the lands for best accuracy, can't get that from any manual.
This is from Accurate Powders Manual.
SPECIAL NOTE ON CARTRIDGE OVERALL LENGTH “COL”
It is important to note that the SAAMI “COL” values are for the firearms and ammunition manufacturers industry and must be seen as a
guideline only.
The individual reloader is free to adjust this dimension to suit their particular firearm-component-weapon combination.
This parameter is determined by various dimensions such as 1) magazine length (space), 2) freebore-lead dimensions of the barrel, 3)
ogive or profile of the projectile and 4) position of cannelure or crimp groove.
From Hornady #7.
Using a bullet specific manual is great, but it is certainly not necessary. It is perfectly safe to use load data of Same Weight and Similar Construction with different bullet manufacturers. If it were not then thousands of bullets like Remington, Winchester, Armscore, Montana Gold, Zero, Precision Delta, Midway, Midsouth, etc.etc. would be worthless as there is No manual to support them.
Case capacity/COAL can and does affect pressure in straight walled pistol rounds. In a bottle necked rifle round, not so much, in fact not at all. What affects pressure in rifle rounds is the distance to the lands, not the case capacity. The shorter the COAL the longer the jump the Less the pressure. Longer COAL will have less of a jump equaling Higher pressure.