There is no rule that states one must load his ammo to maximum length. However, there is a compromise to be struck between several factors: ammo that is too short may not feed well, seating the bullet too far down in the case may raise pressure in these little cases well above acceptable levels, and finally, ammo loaded too long or short may not crimp or hold the bullet properly. Ammo with too little area bearing on the bullet to grip the bullet may allow the bullet to move into the case as the cartridge goes up the feed ramp and that will raise pressure a lot
Still, this is not all that complicated. Usually the bullet manufacturer will have a suggested seathing depth and sometimes other loading manuals can be read to gain an idea of what will work.
The lube line, or the line at the top of the lube groove, usually is completely covered when one loads ammo. Doing so keeps the lube covered and the dirt out of the stuff.
Many times semi-auto bullets are crimped only to the extent that the crimp barely closes the case mouth around the bullet. When that is so, the only tension holding the bullet is the case itself because there is essentially no crimping hold. Those bullets are also susceptible to being forced into the case as the cartridge goes up the feeding ramp of semi-autos and this phenomenon is obseverved occasionally.
Get in touch with your bullet's mfr., and/or get some good loading manuals that deal with those kinds of bullets.
