Nick, try this,
Take enough empty cases to fill the magazine and mark them with felt tip so they cannot be confused with live rounds.
Make up one dummy round using a resized case without a primer or powder and the desired bullet.
Seat the bullet in the case so that the cartridge just fits the magazine, put it into the magazine and see if it will feed from the magazine into the chamber, don't try closing the bolt yet.
If it does not feed easily then progressively seat the bullet deeper until the dummy round will travel easily into the chamber.
Once it does then coat the bullet with felt tip or engineers blue as suggested in previous posts and try closing the bolt then unloading the dummy round and check for any marks on the bullet from the rifling.
If no marks adjust enough dummy rounds to fill the magazine and work them through the chamber as sometimes the first round will feed but the others may not, adjust seating depth until all rounds feed and chamber easily.
You are almost there as you now have the maximum length of cartridge with that particular bullet that can be used in that rifle under field conditions.
However for safety it is prudent to use the comparator to check the distance from the lands and ensure that the bullet ogive is at a safe distance from the lands for that make and type of bullet, but don't make the cartridge any longer as there is no point in seating the bullet closer to the lands as you will not be able to chamber the live cartridge easily in the field.
If there are marks in the felt tip coating then adjust with the comparator until the bullet ogive is at a safe distance from the ogive.
If a bullet sticks in the barrel then use a clean hardwood dowel to tap it out (just smaller than the barrel diameter so it doesn't flex). You can use a cleaning rod however there is a greater chance of damaging the barrel with a metal one.
You can then dismantle all but one of the dummy rounds and reuse the components. the one you keep can later be seated to the depth you find most effective on your reloads so you have a reference for setting the seating die for that load at a later date.
You can also use one of the dummy rounds as a snap cap by getting a bit of hard rubber (pencil rubber or similar) cutting it to fit the primer pocket and securing it in place with glue.
Regards
Bob