I am seating them in the cartridge case at a specific point I have determined from trial and error accuracy testing so that the bullet is exactly 0.028 inches from engaging the rifling in the barrel in my chamber.

The gap is called "bullet jump," from the point of ignition to the point that the bullet actually engages rifling to start the bullet spinning in the barrel. Some rifles are more precise when there is a certain (very small) jump like mine, and some do better with no bullet jump. When there is no "bullet jump" it means that the bullet is "engaged" by the rifling in the barrel in front of the chamber when a round is actually chambered. If you chamber a round in such a rifle without firing or after a misfire and then pull the bolt back to eject the cartridge, the bullet is ripped right out of the cartridge and live fast-burning smokeless powder spills into the (usually hot!) receiver. You never want to do that after firing 30 rounds rapid fire! Sometimes in competition someone will have a misfire/misfeed on the last round from a 30-round magazine, and they will clear the breech and ignite a big flash fire as the spilled high-speed powder ignites from the high temperature of the bolt face and receiver. It is pretty spectacular and really fries off the eyebrows of the shooter. I have never personally witnessed one of these conflagrations, but I have seen video of it and it is amazing.

On the rounds that I make, I start with brand new Remington .223 brass with an overall length of 2.750 inches. I chamfer and ream the new cases and prime them with gold Remington Benchrest primers. I load 77-gr. Sierra Match King Hollow Point Boat Tail bullets in front of Alliant R-15 Powder.

Below is the step-by-step process I go through for these special rounds.

The rounds in the loading blocks, manually chamfered and reamed. You can see the shiny metal where I have prepped the case mouths.	The carbide steel chamfer/reamer is visible at the lower right. Some of the case mouths are a tad "out-of-round" but not enough to matter.
The rounds in the loading blocks. This photo actually shows the chamfer bevel in the harsh flash light.	The rounds in the loading blocks. You can actually see the random pattern of the raw brass in this close-up view.
Chamfer lip close-up, and also a real good view of the randomness of the metallic crystals in a new brass cartridge case.	The 200 rounds in the loading blocks. Prepped and going for the primer stage.
The rounds in the loading blocks.	An interesting wide-angle eagle-eye view of the prepped cases in the blocks.
I use Remington # 7-1/2 Small Rifle Benchrest Primers.	Feeding the primers into the primer loading tube.
Priming the cartridges.	A close-up of the primer before it is seated.
A primed cartridge close-up view.	These are VERY long bullets. Almost twice the length of .223 Rem varmint bullets.
Sierra seems to rule the roost in match bullets.	I bought a box of 500 of them.
Overall cartridge length is ideally 1.750 inches. I am 6/10,000th of an inch over here on the micrometer, which to me is tolerable.	Alliant Reloader 15 is the best overall powder for .223 Rem with heavy bullets.
Taring the scale at zero.	I am using 23.8 grains of R-15 powder for these rounds.
I am trickling individual grains of powder to get it exactly on 23.8 grains of R-15 propellant.	This is as close as I will ever try to achieve to uniform powder weight in each cartridge.
Top-view showing how much powder is in the case. The bullet will compress this powder.	A better view. This gets really close to over-compressing the powder and if it is fucked up you can get wildly huge overpressure.
A view of the bullet resting at the cartridge neck, ready to be seated to a VERY specific depth.	A fully seated bullet in the cartridge.
Close-up of a seated and complete cartridge.	Spec'ing the overall length (OAL) at 2.260 inches, ensuring that it will function in a standard AR-15 magazine.
The beginning of a full block of loaded cartridges.	This took about 2-1/2 hours to get here. I have 30 more minutes to go.
It may look like a lot of work, and it is, but it is also fun and therapeutic. And I have proven sub-0.5 minute of angle (MOA) accuracy rounds when I do this. Expensive? You bet. Time consuming? Of course. Worth it? Absolutely!