I'd like to add something. If I'm wrong or making an incorrect statement, please comment.
John/AussieGunWriter,
In your first post on this thread you mentioned that intial OAL does not matter - but you have to start somewhere. I'm not trying to be a pain or say that's wrong, I'm only trying to add to the discussion.
Initial OAL, generally speaking, should start off with a jump to the lands of .020 or .030 with most bullets. This avoids potential pressure problems with the bullets kissing or being jammed into the lands and it's a good place to start for finding the best accuracy, generally speaking. This is dependent on whether or not magazine length will allow this. Bullets should not be seated so far out that the bullet is no longer held inside the neck by at least 2/3 of the bullet diameter. Some say not less than a full bullet diameter. Bullets should also not be seated so deep in the case that the tapered portion is inside the neck, it's rarely the case, but noteworthy when later adjusting seating depth.
Some factory rifles with a given bullet will not be able to be seated even close to the lands. Weatherby cartrdges and other magnums with free bore or a long throat makes this impossible. Some non magnum factory rifles just have a long throat just to avoid pressure issues with so many variables in factory ammo. In that case you could use the maximun allowable magazine length as a starting point. Another place to start would be the recommended OAL in a manual that lists that specific bullet.
If you have a rifle that shoots factory ammo very well and are trying to duplicate a handload with the same bullet, starting at the same OAL would be a good choice. This also could be an indication that your rifle is not so finicky about OAL.
As you said, Barnes bullets seem to be an exception to seating close to the lands. Barnes recommends starting .050 off the lands. Some folks find that seating them even further out results in best accuracy.
If you're developing a new load with only a different powder, start at the same OAL that had previously given good results. If using a different bullet that has a very similar ogive, or profile, using the same distance to the lands would make sense.
If you have a cartridge that requires crimpimg into a groove then none of this applies.
All rifles are different. Some will shoot accurately with a long jump to the lands, others a short jump, some are not so fussy and some rifles will show a huge improvement with getting OAL just right. When developing a load do not change anything but powder charge and when the best accuracy node is found then it's time to start fiddling with OAL.
These are my thoughts on this and hopefully it adds something to the discussion.
fish head
