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Have you been wondering how to find the bullet seating depth for best accuracy in your rifle? In this article I’ll go over how you can fine-tune the bullet seating depth to achieve even greater accuracy. Hopefully by the end you’ll be able to take this knowledge and tighten up those groups.

The way to achieve the bullet seating depth for best accuracy in your rifle is to determine how far off of the lands of your rifle to seat the ogive of the bullet.

What are the lands of a rifle?

The lands of the rifle are where the rifling of the barrel starts. If you have a bolt action rifle, you can remove the bolt and look from the rear of the rifle out the front of the barrel. You will see some spirals in the rifle barrel. The spirals give the bullet spin and help it to be more accurate.

What is the bullet ogive?

Also, worth noting to everyone else.this is a picky rifle and the accuracy between nodes has been significantly different.ranges from 4MOA down to.6MOA with simply changing powder amount and nothing else so I should be able to see immediately if this holds true (for my current load/rifle that is). Sep 11, 2014 #17.

The bullet ogive pronounced “oh-guy-ve” is the front section of the bullet where it starts to curve towards a point. You can see where this is in the below picture.

My best example of this is using Pyrodex RS on a clean barrel with a Knight Wolverine. The first shot out of a clean barrel can be as much as 6' out of the group at 100 yards. With that first fouling shot on the barrel, 1' groups are very common but on a clean barrel, that first shot can be anywhere in that 12' circle.
Break In Your Rifle Barrel. Most hunting rifle barrels have not been properly broken in, which helps to minimize accuracy-reducing fouling. If not properly broken in, we have observed hunting rifles to completely foul out in as little as five rounds. Many will foul out at fewer than 20 rounds. When a barrel fouls out, accuracy is dramatically.

Why is the bullet ogive so important?

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In the course of reloading you will notice while looking at reloading recipes that the COAL often gets mentioned. The COAL is the cartridge overall length. It is measured from the base of the cartridge to the tip of the bullet. This measurement is important to make sure that your cartridge will load properly into a magazine. However, length of individual bullets can vary. For example, I took 6 different rifle bullets from the same batch and measured them. Below are the lengths I found:

1.4035″
1.403″
1.400″
1.405″
1.403″

Try it with a random sampling of your own bullets.

Because the length of the bullet can vary slightly across all bullets, there is another measurement that is helpful in order to obtain the bullet seating depth for best accuracy for the bullet you are shooting. This measurement is known as the CBTO.

What is CBTO?

CBTO is the Case Base to Bullet Ogive. Your bullet length may have variations. The ogive is going to have much less variation. This means that we can use it to determine a more consistent seating depth for the bullet.

Using Ogive to Determine the Bullet Seating Depth For Best Accuracy

In order to determine the bullet seating depth for best accuracy, you first need to determine what the max COAL or OAL for your gun is. There are a variety of ways to do this.

OAL Length Gauge

Hornady makes an OAL length gauge. You can find it on Amazon here: Hornady OAL Gauge. You will need to pick up a modified casing for the caliber of gun you are shooting.

This gauge is used by attaching the modified case to a rod and then inserting one your bullets into the case. The case is then inserted into the rear of the rifle and the bullet is pushed forward until it barely hits the lands.

If using this method it is important to measure using the exact same bullet every time. You may notice overtime as you shoot your rifle more more the lands will wear down and retreat somewhat. This is because the more you shoot the rifle the more the explosive energy of the cartridge starts to wear away at the rifling at the mouth of the barrel.

As there can be some variation in bullets you want to make sure you use the same bullet every time if you are using this method. If you are shooting a .270 and shoot bullets from two different companies, you will want to do the same for each brand. Each brand will have a slight variation on their bullet. Keep one bullet from each brand to reuse each time you measure the OAL for your rifle.

One thing you will want to do is make sure the base of the shell to the tip of a trimmed casing that has been fired from your is the same as the modified bullet in Hornady OAL kit. If it is not, you will need to adjust your calculations to take this into account.

In the process of using the gauge you, may find that the bullet becomes stuck in the barrel of the gun. You can use either a cleaning rod to gently tap out the bullet or place the gun with the butt on the ground and gently tap it. Either way should cause the bullet to come free.

Curved OAL Gauge

If the gun you’re using does not allow the bolt to be removed or there is now way to get rear access to the chamber, then you can use a different version from Hornady that is curved.

Lower Cost OAL Gauge

Frankford Arsenal makes a lower-cost version of an OAL gauge however this one is made of plastic: Frankford Arsenal OAL Gauge. It also costs less than the Hornady version.

I figured out the OAL of my gun, now what?

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Now that you know what the max OAL of your gun is, you can start to adjust bullet seating depth either closer into the lands or away from the lands.

Two terms you will want to be familiar with when adjusting the bullet seating depth are jam and jump. These relate to whether the bullet is seated further into the rifling or away from the rifling.

Jam – A jammed bullet is a bullet inserted further into the rifling of the barrel beyond the initial point where it touches the rifling. You can remember this by thinking of the bullet being jammed further into the rifle barrel. You need to be extremely careful when using a jammed bullet because this can cause greater pressure than what normally would be present. Also, if you are hunting or in a situation where you want to remove a cartridge from the chamber without firing it, a jammed bullet may stay stuck in the barrel. The bolt could pull the casing free from the bullet.
Jump – A jumped bullet starts further back from the lands of the rifle barrel. One way to remember the meaning of a jumped bullet is to think that the bullet has to jump a little bit before it reaches the opening of the rifle barrel.

Adjusting the Seating Depth

Once you figure out where the lands are in relation to the ogive of your bullet, you will most likely want to start 0.015” to 0.020” back from the lands. At this point you can start to adjust the seating depth of the bullet and notice how it affects the accuracy and grouping of your rounds.

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After shooting a group and examining the accuracy, you can increase or subtract 0.005″ and go from there. If you are putting more of a jam on the bullet make sure that you are using a lighter load as a jammed bullet causes higher pressure in the chamber. Keep adjusting the seating until you find the bullet seating depth for best accuracy in your rifle.

Using a Bullet Comparator

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In order to measure where the ogive should be in relation to the lands, you will need a tool known as a bullet comparator. Hornady also makes one of these: Hornady Comparator. It comes with a variety of gauges for different diameter bullets. The previous link comes with a set of 14 inserts for measuring different calibers. It will measure from 17 to 45 caliber. Another nice accessory to have is the anvil base kit from Hornady: Hornady Anvil Base. This attaches to the other arm of your calipers and provides a wider base for the casing to rest on when measuring the ogive.

After determining your CBTO based on how far away from the lands your bullet ogive should be, you can set up your press to seat the bullet. Then use the comparator tool to measure and make sure the cartridge base to ogive(CBTO) is where you are expecting it to be.

One thing to also consider is that you want to leave at least the width of the bullet in the casing. So for instance if you are shooting a .284″ diameter bullet, leave at least .284″ of the base of the bullet inside of the shell casing. This will help to stabilize and seat the bullet.

Quick Recap For Obtaining the Bullet Seating Depth for Best Accuracy

Find the OAL for your rifle using an OAL gauge. Then you will know where the lands start and then you can start to play with the CBTO for your rifle chamber. Make sure that if you are using Hornady’s kit, that you measure their modified casing and a trimmed brass casing shot from your rifle. There may be some difference here.
Seat the bullet with the ogive starting at 0.020″ from the lands or rifling of the barrel
Start increasing or decreasing 0.005 in at a time until you achieve the grouping you desire. Be careful if you are putting a jam on the bullet as this will caused increased pressure. You don’t want to start with a max powder weight if you are using a jammed bullet.
In order to measure the CBTO, use a bullet comparator tool
Have at least the width of the bullet inside the casing. So if you are shooting a .284” diameter bullet, keep at least .284” of the bullet seated inside the shell.

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