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In a RIFLE (as compared to a hangun) cartridge, the pressure is usually more a matter of how far the bullet is from the start of the rifling, rather than how far it is seated into the case. A least, that is the concern with making cartridges longer than indicated by the pressure-tested data. The distance to the beginning of the rifling varies a lot from gun to gun, and even changes on the SAME gun as the throat wears/erodes from use. So, the real issues are going to be specific to YOUR gun. And, specific to the particular bullet model number that you are using, because the distance back from the tip of the bullet to the place where it contacts the rifling varies a lot from bullet model to bullet model.
To find-out how long you can load a cartridge in your own gun, you need to gently push the bullet into the rifling from the chamber to see where it touches. There are some tools you can buy to do that. Or, you can use either of two "home brew" methods.
One method is to make a case that holds the bullet just firmly enough to let you chamber it with the bullet seasted way out in the case neck and have the rifling push the bullet back into the case just far enough to let you extract the case and measure the COL without the bullet slipping.
The other method is to get a friend with a pencil hold the bullet gently against the rifling while you push a cleaning rod down the bore from the muzzle and mark it where the muzzle is when it is contacting the bullet. Then remove the bullet and close the action, push the rod down the bore again until it stops at the breech and mark the rod again. Then the max COL is the distance between the marks on the rod.
Both methods have their problems. With the modified case holding the bullet, it is important that it is not held so tightly that the bullet is rammed part way into the rifling, but not held so loosely that the bullet slips in the case when you extract and measure it. With the cleaning rod method, it is important that some sort of flat tip be used on the rod so that a pointed bullet nose doesn't go into the rod a bit and make the resulting measurement too short.
Once you know how long a cartridge CAN be, you still need to decide how l ong you WANT it to be. Accuracy is usually affected by the distance that the bullet travels before reaching the rifling. And, different bullets work best with different distances. Sometimes there are ttwo distances that work, one pretty close to the rifling and one pretty far away.
Another issue with max COL is whether you want the cartridge to fit in a magazine. In many rifles, the magazine length will keep you from loading bullets long enough to reach the rifling. In rifles with long "free bore" (especially Weatherbys) it may not be possible to touch the rifling with the bullet and still have the bullet seated into the case at all.
So, the first step is to find out how the rifling is on YOUR rifle.
SL1
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