RC is right. With lead bullets in semi-autos, your barrel will determine OAL. This is because lead bullet ogive profiles are all over the place, a fact I learned the hard way.
Use a bullet and an unprimed case to determine the longest OAL (shorten and test the round in tiny increments and remember that a taper crimp may also be required) that allows the round to drop into and fall out of your barrel. Now shorten it by a couple thousandths to get it off the lands. Check to make sure it will fit in your magazine and will chamber from the mag.
Now you have a functionally-sized dummy round loaded with your desired bullet. It might be considerably shorter than any other round you've loaded. You can use published or self-tested load data to start, and adjust accordingly as follows:
Take a trusted low-moderate power jacketed load and measure the length of the completed round (you should have this recorded). Now measure the length of the bullet used in that round. Subtract the bullet length from the OAL; that's the distance from the case head to the base of the bullet inside that trusted round. Let's call that number CH-BB.
Now do the same with the dummy round you just made. Is the CH-BB of your dummy round shorter than your trusted round? That means you'll need to adjust the powder load down by about the same proportion.
For example, if CH-BB of the trusted round is .800" and CH-BB of your dummy round is .720", you have roughly 10% less useable case volume in your dummy round and should use about 10% less of the same powder to achieve the same pressure. And since the trusted round was jacketed and your dummy is lead, adjust the charge down by another 5-10%.
If the dummy round's CH-BB is xx% longer, adjust the powder charge up by xx% and then down by 5-10%.
This method assumes similar base shapes for the two bullets and does not take into account the fact that the web portion of CH-BB does not contribute to useable case volume. But since you started with a low-moderate power load, it gets you close enough and is safe.
