How to Seat Bullets Precisely
January 04, 2011
Hornady's overall-length gauge with modified case, bullet comparator assembly, and dial caliper together will precisely determine the ogive-to-case-head dimension so that you can adjust your seating die accordingly.
When I began writing this column, we changed the name from "Precision Reloading" to "Practical Reloading." If you noticed, you may have wondered, "Why?" The reason's simple. I'm an engineer by training and experience. Typically, my approach to accomplishing a task or solving a problem is to determine a workable and, preferably, simple scheme. So characterizing the human genome would surely bore me to death--even if I had any idea how to do it. I apply these same engineering methods to handloading with usually safe and satisfactory results.
However, paying special attention to a specific detail can help ensure optimum performance. For example, I always prep rifle brass primer pockets. Properly seating primers means each one will ignite consistently, and uniform internal ballistics often lead to improved performance.
Another factor that can significantly affect a handload's accuracy is the position of the bullet relative to the throat leade--i.e., the initial tapered part of the rifling. Conventional wisdom holds that accuracy is best if the bullet is almost touching the rifling when the cartridge is chambered. The concept is logical if you consider that the bullet is essentially constrained between the case mouth and the rifling, so when it begins to move, it remains precisely aligned with the bore.
When I first started to reload, I read about how to seat bullets correctly. Many earlier loading manuals noted how deep to seat the bullet into the case. Of course, because you can't see the heel of the bullet when it's inside the neck, you had to measure the bullet's length, subtract the specified seating depth, add the case length, and then adjust the overall cartridge length accordingly. Today's manuals typically specify cartridge overall length (COL) instead of the bulletseating depth.
The chamber shape for any specific cartridge varies from one firearm to the next, so depending on the specific throat and leade dimensions, the bullet may need to be seated farther into the case in order to not jam into the rifling. Of course, if a rifle has a box magazine, the absolute maximum overall cartridge length is constrained by the magazine clearance--unless you want to use it as a single-shot.
Back when I started, I determined maximum COL by inserting a cleaning rod with a flatnose jag attached into the bore until it touched the boltface. Then I wrapped a piece of masking tape around the rod at the muzzle to mark how far it entered the barrel. Next, I opened the bolt, stuck a bullet nose-first into the throat, and reinserted the cleaning rod. Using my finger to hold the bullet firmly in place, I wrapped another piece of tape around the rod at the muzzle.
By measuring between the two pieces of tape, I had the maximum COL for that specific bullet in my rifle. The relative precision of this method depended greatly on whether someone else applied the tape while I held the rifle steady and kept the bullet firmly in place.
Next, I adjusted the seating die stem to obtain the desired COL. Of course, proper quality control requires that you spot-check the cartridge length occasionally using a caliper. Quite often, it varied plus or minus a few thousandths of an inch even if I seated each bullet carefully. Pretty soon, I learned the shape and condition of the bullet tip significantly affected the measurement. I often had to adjust the stem to ensure that the COL was consistent yet within the magazine limit.
With the overall-length gauge inserted firmly into the rifle's chamber, push the bullet into the rifling with the adjustment rod and lock it in place with the thumbscrew.
Then I discovered the best way to determine and verify proper bullet seating. This method uses the bullet ogive instead of the tip. Practically speaking, the forming die that swages the final bullet profile yields a much more consistent datum at the ogive than the nose. The bullet tip doesn't engage the rifling, so why set the COL using it as the point of reference?
Hornady's Lock-N-Load Overall Length Gauge used in conjunction with the company's caliber-specific comparator/bushing attached to a caliper will ensure that the bullet is seated precisely where you want it. The gauge is comprised of a hollow tube threaded on one end to accommodate mounting a specially modified cartridge case. A slender plastic rod contained within the tube adjusts the bullet's position in the case mouth.
Using the overall-length gauge is quite simple compared to the crude scheme I described earlier. First, you remove the bolt to gain clear access to the chamber. If you have a semiauto or lever-action, open the action and use Hornady's curved L-N-L Overall Length Gauge. Screw the special modified case onto the tube tightly so the subsequent measurement is exact. Then adjust the rod position so you can place the bullet into the case mouth far enough so that it cannot engage the rifling.
Before proceeding, make sure the gun is unloaded and the chamber is clean and dry. Oil or powder residue remaining in the chamber will prevent the case from seating properly and cause an incorrect reading. Using the tube, insert the modified case into the action and firmly seat it in the chamber. While securely holding the tube/case assembly in place, push the adjustment rod until the bullet ogive engages the rifling. Lock the rod with the thumbscrew mounted on the sleeve at the end of the tube.
To remove the gauge, you can either carefully pull it out, or you can use a wooden dowel or cleaning rod to gently tap it free if the bullet binds in the rifling. If the bullet is disengaged from the case during this step, simply reinsert it into the case mouth and measure the overall length. The locked adjustment rod will ensure that it seated to the correct depth. Of course, one reading is not likely to be absolutely correct, so take several using multiple bullets to obtain an optimum max overall length.
As Hornady's instructions clearly describe, your technique using the gauge can easily affect the results obtained. Again, consistent, repetitive actions lead to more uniform and accurate measurements. If you're loading a plastic-tipped or FMJ bullet--i.e., one that's not easily damaged--you can simply measure the overall length without further ado. However, if you're loading a softpoint bullet or you want to be as absolutely precise as possi
ble, continue to the next process.
Hornady's bullet comparator kit includes a universal body and several caliber-specific inserts. Select the caliber you're loading, attach the insert to the body, and then attach the assembly to the moveable blade of the caliper. Close the caliper until the comparator body/insert assembly is sandwiched between the blades. The reading should be close to 1.000 inch, and if you're using a dial caliper, you can adjust the dial to that setting.
Open the blades enough so that you can place the bullet--previously positioned in the modified case--into the comparator insert and the fixed blade into the slot in the overall-length gauge behind the modified case. The caliber-specific insert engages the bullet ogive so that you can take a more precise measurement. Record the ogive-based overall length and repeat the procedure as many times as you need to assure that you're confident with the results. Again, as with using the overall-length gauge, your consistent actions help ensure consistent results.
Using the results from the overall-length gauge--with or without the comparator kit--you can now adjust your seating die so the bullets do not exceed maximum allowable length. Don't forget the magazine limit! If you're shooting targets, seating the bullet so it touches the rifling may be your best option. However, hunting ammo should have the bullets seated deep enough to ensure absolutely reliable feeding.
Practically speaking, different bullet brands and types of the same caliber have various profiles. Hornady's overall-length gauge and comparator kit have fixed dimensions that will be more compatible with certain bullets than others. In addition, the modified case may not exactly match the headspace of your rifle. As always, this simply means the final proof of the pudding is how your handloads perform at the range or in the field.
However, these Hornady Lock-N-Load tools will help the competent handloader fully explore and understand another important factor affecting accuracy--i.e., where the bullet starts will surely affect where it strikes.