Reloading is always a good idea, and I am finding it even more useful these days. It is darn hard to find ammo of any sort, let alone the specific bullet and weight you want. If you keep stocked up on components you have a lot of options.
Right now I can easily go shooting anytime I want and shoot a few hundred rounds of rifle and pistol ammo and have it all reloaded a couple of weeks later. I could use my 5000 small pistol primers to load any combination of .38 Special, .380ACP, 9x18 Mak, 9mm, or .40S&W. I can use my several pounds of Varget and H4895 powder to load any combination of common bullets in .223, .308 or .30-06. I can use my stockpile of various .308" bullets for either .308 Win or .30-06.
Friends and relatives in other areas can't even find one or two boxes of a single cartridge, or it costs $40 a box if they do find one. In fact, I am helping a SIL load up a few hundred each .223, 9mm, .44 mag to take ot a family shootfest next month. His brothers can't find any ammo on the shelves. I have several thousand primers, many pounds of powder, and several thousands of bullets and brass on hand.
Bullet seating is easy. Get a reloading manual and make sure it gives the maximum cartridge length, which is usually indicated on the bullet diagram. You do not want to exceed this length otherwise it may not fit properly in the chamber and could increase pressures dramatically if it etends into the throat.
Next, every data table for powder loads should specify the cartridge overall length that was used to test the powder charge. Do not seat the bullet so that the overall length is LESS than this. That would decrease the space within the case and also could increase pressures dramatically. You can seat at this specified length, or any length out to the maximum length. Cartridge overall length is abbreviated in tables as COL (Cartridge Overall Length) or OAL (OverAll Length).
Lastly, you want to take into consideration the type, weight and construction of the bullet you are using versus the ones used in the data tables. Heavier bullets are "usually" longer. However, non-lead bullets such as all copper or hollowpoint or polymer tipped bullets are usually longer than equal weight all lead jacketed bullets. Either find data for the specific bullet you have (Nosler, Barnes, Sierra, Speer all publish reloading manuals), or use the data for the next weight up if you are using an atypical bullet.
For instance, if you can only find data for a plain Jane 150 gr. .308" jacketed soft point or FMJ bullet, but you are loading a Nosler Ballistic Tip 150 gr. bullet, then I would recommend using the data for the plain Jane 165 gr bullet since it is more similar to the length of the 150 gr ballistic Tip. DO NOT load a 150 gr Ballistic Tip or Barnes STX bullet to the same powder charge and COL as you would for a typical Speer 150 gr. SP.
If you keep those three factors in mind (max COL as the maximum, tested COL as the minimum, and adjust for atypical bullet type) then you will have your ideal COL range.
Then you just seat your bullet such that the COL is within that range. You adjust the bullet seating by starting with the seating bplug screwed out quite a ways. Then you screw it in a 1/4 turn and check the length. Repeat until COL is in the target range.
Clear as mud?
