PrecisionRifleBlog.com A DATA-DRIVEN Approach to Precision Rifles, Optics & Gear
One of the benefits of reloading your own ammo is that you can customize it to your chamber. Factory ammo must function in every possible rifle, but the ammo we handload can be fine-tuned to our specific rifle – and often that can improve performance.
This page explains a method to precisely measure the distance to touch the lands on your rifle. That would tell you how far out you need to seat the bullet in a case to contact the lands. Learn more about bullet jump and recommended best practices.
Mark Gordon from Short Action Customs told me about this measurement method, and I’ve used it to measure barrels for various cartridges from 6mm to 338 and found to be very precise and repeatable within 0.001”. In fact, I’ve performed the measurement back-to-back, running through this entire process once and found the distance, then I sat that cartridge aside, and repeated the full process again on the same barrel. After I finished the second time, I measured the Cartridge Base To Ogive (CBTO) distance for both cases with bullets seated in them and they were identical down to the thousandths place.
I’ve used other methods to as I tried to customize my seating depth for a particular rifle in the past, including what most shooters probably do, which is simply closing the bolt on a loaded round and seating the bullet incrementally deeper until there were no longer rifling marks on the bullet. I’ve also used the Hornady Lock-N-Load OAL Gauge to determine the distance to the lands. While other methods may be able to get you in the ballpark area of what the distance is, they aren’t near as accurate or repeatable as Mark’s method (or the another good method from Alex Wheeler that I’ll also mention late in this post).
Now, I will say this method is a little bit of a hassle because you must remove the barrel from the action. If you’ve never done that before, with the right tools (i.e. barrel vise, action wrench, and torque wrench) you can typically do it in under 5 minutes. So, it’s not too inconvenient.
Here is a video that walks you through the entire process. I also typed out the instructions below for those who might want to print them out for reference.
Here are the typed out instructions for how to measure the distance to the lands on your rifle barrel:
Step 1
You need to resize a case, and make sure you size it enough that it drops all the way into the chamber and headspaces on the shoulder without having to apply any additional pressure. It should just drop all the way into place with gravity alone.
Step 2
Seat whatever bullet you are going to use into the case. I typically start with a CBTO that is much longer than what my distance to the lands is likely going to be.
Drop the case with seated bullet into the chamber, and gently tap it with your finger to make sure it’s seated snuggly. If it didn’t drop down to the same spot as where the empty case was, we know the bullet is seated into the lands and is keeping the round from seating fully in the chamber.
Even though you only lightly tapped the round into the chamber with your finger, it will be slightly difficult to extract, because the bullet is engaged in the lands. If you try to remove it using only your smallest fingernail, you shouldn’t be able to extract the round. In fact, you may not be able to do it with your bigger fingernails. No worries. Just use a pair of tweezers or a flat head screwdriver to very lightly pry the case of the chamber.
Step 3
Go back to your reloading press and seat the bullet slightly deeper and then retry. You may have to do that a dozen times to arrive at the perfect seating depth to barely touch the lands.
As you try different seating depths, you will eventually notice the case is getting closer and closer to seating all the way into the chamber like your empty case did. When I first start out, I might make 0.005-0.010” of changes in my bullet seating depth each time, but once it starts getting close you need to switch to only making very slight changes in seating depth each time, like 0.001” each time. A seating die with a micrometer is handy here to help you dial in those small adjustments in seating depth.
You need to repeat the process until you can lightly tap the round into the chamber with your finger, and then easily extract it multiple times using only your smallest fingernail. If you can extract it with only your pinky finger sometimes, but not 100% of the time … you are very close, but not quite there. Seat the bullet 0.001” deeper and then try again.
Once you’re able to extract it multiple times with very light pressure using only the fingernail on your pinky, that round is now your distance to your lands. That means if you loaded ammo to that COAL (or better yet CBTO – learn why), then the bullet would be in very light contact with the lands. Some people call this “kissing the lands,” because it isn’t jammed into the lands and you also have 0.000” of bullet jump.
Now What?
I’d suggest taking out your calipers with a bullet comparator on them and measure the distance from the cartridge base to the ogive (CBTO) of the loaded bullet, and write that number down as a reference, along with the current round count of the barrel.
Now that you know your distance to the touch the lands, I’d suggest doing some load development to see what kind of seating depth works best. If you wanted to try 0.010” into the lands or 0.040” off the lands, you’d just offset those amounts from the distance to the lands you just measured. Berger Bullets has a great recommendation for fine-tuning your seating depth, which you can read about here: Getting the Best Precision and Accuracy from VLD bullets in Your Rifle.
Keep in mind that on most rifles, this measurement changes by 0.003-0.010” every 100 rounds as the barrel wears and the lands erode. So, if precise bullet jump is important to you, you’ll likely need to repeat this method periodically and regularly adjust your seating depth to keep that same relative bullet jump to the lands. You may here other shooters refer to that as “chasing the lands.”
The Alex Wheeler Method
Finally, I’ll mention that Alex Wheeler, from Wheeler Accuracy, also has a very precise and repeatable method to find the distance to the lands. Alex’s method works without having to remove the barrel, but you must disassemble the bolt, and it’s more involved than just removing the firing pin. You must do that, so you have a more precise feel when you close the bolt, otherwise you wouldn’t be able to sense when the bullet engages the rifling. To me, removing the barrel is faster and easier, so I use Mark’s method, but which is easier likely comes down to the particular brand of action you’re using, and how easy it is to remove those parts. You can watch Alex’s video demonstration below to see what all is involved.
