Just started reloading and am as confused as Joe Biden!!! The first few loading sessions have gone smoothly but I was loading to the COL SAAMI length because I thought that was a standard length to fit per the caliber and was a SAFE length that the factories use. I have now noticed in my Hornady book that there is a different COL recommendation for each size/wgt category of bullets listed at the top of the loading info. I have not started dealing with chasing the lands yet because I am still getting comfortable with the load procedures at this point. When you start chasing the lands do you ignore the book recommendation? And I have noticed when I do go by manufacturers COL I end up right at the cannelure. Is this necessary and how can it be done if you are moving the bullet in and out to adjust jump and relative land position? I am loading for several calibers and they all have deviations according to bullet size.
Thanks for your help
You didn't say what types of guns you're reloading for (e.g. Bolt Action, AR's, other semi-autos, combination of them), as responses for each can be quite different one from the other. . . ???
First, I'd recommend you don't get in the habit of thinking in terms of jump. While it's good to know just where the the lands is, that distance is just most useful so that you don't load your cartridges to touching the lands, which can cause a huge pressure problem. If you're only feeding from a mag, then going to be a non-issue in factory guns built to SAAMI specs. Rather than thinking in terms of jump, think in terms of seating depths. You definitely don't want to be "chasing the lands" in any way.
When you're "moving the bullet in and out", you're changing the seating depth, which is what has a much greater effect on your load performance than the distance to the lands. This is easy to understand as you see your chamber's throats erode over time, which means you distance to the lands is always growing in length, yet your good load's performance continues.
So, the answer to your questions is that you NEVER "chase the lands", though you may at some point change your seating depth when you see your precision/accuracy on paper changing in order to bring it back. What seating depth you eventually use for best performance will depend on various factors, like the particular bullet you're using along with powder, brand of case you're using, how tight the bullet is being held by the neck of the case ("neck tension"), temperature, etc.
Keep in mind that "seating depth" is how far the base of the bullet is from the base of the case, which determines the volume the expanding powder burn gets to work in. Different bullets have different dimension so their OAL effects both distance to the lands as well as their seating depths. Even though a bullet's OAL often have significant variance, reference to the COAL's is the best way to comminate one's seating depth. Because different chambers are different sizes along with various throat erosion and that the caliber inserts used to measure jump have significant variations in their measurements, it's best not to communicate the jump you might have as it's just won't really tell anyone anything what your seating depth is like or even your COAL.
When one starts reloading, it's a very good idea to load within the SAAMI COAL specs and work up a powder load that performs best. If you then want to experiment with seating depths, one can start a little longer to work up a powder charge so that there's room for shorter seating depths without being concerned over compressing the powder charge.
Since you're just staring to reload, I'd highly recommend you seek out a mentor who's a well experienced reloader. Such a mentor will shorten your learning curve, saving you time and components as you learn what works well for you. You can find them at a range or club where you shoot, just don't by shy as there are many experience shooter more than willing to be of help (much like you see in this forum).
