Measuring Seating Depth Savage LRP 260 Remington

How to Measure Bullet Seating Depth


The question of how long to seat a bullet in relation to the barrel’s rifling is an important one. Seating depth can have a lot of influence on how well your handloads perform. Knowing how to measure for it is an essential skill.

Luckily, it’s not that difficult. With a few basic measuring tools and some practice, we can accurately and consistently measure how far it is from the case’s head to the barrel’s rifling. We use that measurement to find the ideal seating depth for our rifle during load development.

In the video below, I’ll explain and demonstrate my process for measuring maximum Cartridge Base to Ogive Length (CBOL) and throat wear. I’ll also go over some considerations such as magazine length and where I like to start for bullet seating depth when I’m developing a load.

I’ll recap and highlight the important stuff after the video, and provide links to the tools I use for measuring seating depth. You can view the video right here, or click on the YouTube logo to watch it on our channel. Feel free to check out our other videos and subscribe to the channel while you’re there.

The two measurements discussed in the video are Cartridge Overall Length (COAL) and Cartridge Base to Ogive (CBTO). Both need to be considered when seating bullets.

COAL is measured from case head to bullet tip. CBTO is the measurement from the case head to where the bullet contacts the barrel’s rifling. The action and magazine length determine the maximum COAL. The Savage LRP shown in the video was engineered to allow the bullet to contact the rifling before running out of magazine length. Not all rifles work that way, so it’s important to know both measurements.

It should also be pointed out that reloading manuals base load data on SAMMI COAL specs. That’s an important consideration when basing your powder charges on that data. In any given caliber, the weight of the bullet will determine its length. The SAAMI COAL doesn’t differentiate between light and heavy bullets, it just lists one length.

Bullets used for long range shooting are typically on the heavy side and have long nose profiles. If you load them to SAAMI COAL, the bullet will be seated quite a bit deeper in the case than a lighter bullet. That bullet is now taking up case volume, limiting the amount of powder that can be used. It’s also likely to be jumping quite a distance to the rifling.

If the CBTO and magazine length will allow it, seating the bullets shallower will allow more powder to be used. This creates a lot of opportunities, and should explain why load data from experienced handloaders quite often doesn’t match “book data”. Before dumping more powder into the case, please realize there is more to a safe load than bullet seating depth. Proceed slowly, use a chronograph, and learn how to read pressure signs.

A question that came up soon after the video was published had to do with technique when checking maximum CBTO. Specifically, how much pressure to apply to the bullet when contacting the rifling.

As I mentioned in the video, this measurement is a relative value. It’s meant to be used as a comparative number to track throat wear and set optimum seating depth. The shape of the bullet’s nose and how it contacts the lands of the rifling will affect the “feel”. The more you use the overall length gauge, the more comfortable you’ll get with the readings.

I push lightly on the rod until it stops, then hold it there while tightening the screw. The bullet will usually stick in the rifling, more so when measuring with VLDs. Inverting the rifle and lightly tapping the butt of the stock on the bench should dislodge it. I usually take two or three readings and write them down. If they match, I know my technique is repeatable.

The most important things are to make sure the bullet moves freely in the neck and use the same bullet insert for every reading. Practice taking measurements until you’re comfortable with your method.

Overall Length Gauge and Modified Case

Overall length gauge with modified case.

For detailed information on the comparator and inserts, click HERE. I’ve been using the same Mitutoyo (CD-6” CSX) electronic caliper for a long time now. I highly recommend it. Just about everybody stocks the Hornady OAL Gauge and modified cases. If you want to make your own modified cases, the tap size is 5/16”x 36 tpi.

Knowing how to consistently and accurately measure bullet seating depth is a critical step in the reloading process. The methods I used in the video and explained in this article are the same ones I use for every rifle I handload for. Give them a try and see if they work for you!

 

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Sam

As an Idaho native, avid hunter, and long range shooter, Sam has written numerous articles and gear reviews for various online publications. Specializing in long range hunting in the mountains of northern Idaho, Sam founded Panhandle Precision as a way to continue sharing his passions.

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16 Comments

  • Stuart A. Smith
    March 5, 2017 at 10:10

    must be a bad winter in Idaho lol

    • Sam
      Sam Millard
      March 5, 2017 at 10:23

      It’s certainly dragging on! It was snowing again this morning. I’m ready for spring.

  • Todd B
    March 5, 2017 at 14:41

    Thanks for the excellent video description! I’ve been using the “lite-press-fit of the bullet” technique but I might have to get me one of those gauges you use. I can see where that would give a more sensitive measure of when the bullet is just touching the rifling.

  • John Swint
    April 25, 2017 at 11:33

    Sam,
    When making your own modified case, do you set back the shoulder or leave it as it came out of the rifle? I am building up a savage Lrp in 260 and am waiting on the tap to make a modified case. Looking forward to your review of your savage lrp.
    Keep up the good work!

    • Sam
      Sam Millard
      July 12, 2017 at 17:06

      I run the case through a body die or FL bushing die with the bushing removed. It makes it much easier to ensure the shoulder is contacting the chamber. I’ve much much better consistency with this method.

  • Mark Rineer
    July 12, 2017 at 16:54

    Sam you stated for seating depth your starting point is .0010 off the lands. Next do you step closer to the lands? If you step towards the lands is your stoping point @ the lands? I appreciate your knowledge and the ability to clearly teach others. Thank you, Mark

    • Sam
      Sam Millard
      July 12, 2017 at 17:08

      I start at .010″ off. I always go further out before trying at the lands. I’ve only had one barrel that I can recall, that liked to be close. I never jam into the lands.

  • Scott Dodd
    November 7, 2017 at 18:26

    Hello Sam,
    I’m new to this forum,so if this question is in the wrong place forgive me.What criteria do you use for case selection,and do you sort before or after any work is done to the case,such as trimming ect?Thanks,Scott

    • Sam
      Sam Millard
      November 7, 2017 at 19:57

      Most of my process is in “New Brass Prep”. 1-2% is a generally accepted tolerance when weighing cases. I would definitely trim them before weighing.

  • Rene' Ledezma
    January 19, 2018 at 08:14

    Hi Sam great videos I am learning a lot from them. Just looked at your last one about the primer pockets. RCBS Lyman and Hornady make a tool that is called. Pocket uniforming cuter. Keep up the good work thank you for the videos

  • Rene' Ledezma
    January 19, 2018 at 08:17

    Hi Sam keep up the good videos. I just got into long range shooting I had been reloading for several years for planking and handguns. This is new to me so I am trying my best. The tool you were showing on your video is called a pocket uniforming cutting tool. They are made by Hornady Lyman and RCBS not very expensive. Keep up the good work on the videos and I am learning a lot. Thank you Sam hope this is helpful to you or other viewers.

  • Todd B
    January 19, 2018 at 12:28

    If you are trying to make a Berger VLD shoot what size steps do you decrease COAL?
    Thanks — Todd

    • Sam
      Sam Millard
      January 19, 2018 at 12:43

      I usually move in .010″ increments with any bullet I’m trying. If I don’t find a spot within a .100″ bracket where they’ll shoot, I’ll probably abandon the bullet. That’s assuming I’ve exhausted powder and case neck tension options.

  • David Bartl
    January 31, 2018 at 17:39

    Sam, great job on all your vids. I’m in the process of building my first LRP Remington in 7mm-08 and I find that the information you provided is invaluable. You have saved me so much time and money . Can’t thank you enough!

  • Mike Musser
    February 9, 2018 at 11:57

    Sam,

    Thanks for all the great information you are putting out there. After watching your video on bullet seating I am running into mixed results using the COAL gauge. I have taken dozens of reading trying to figure out my barrel on a SAVAGE 110 FPC .338 LAPULA MAG. I keep coming up with different readings. ( 2.907,2.905,2.903,2.910) 2.910 seems to be the most common reading. Am I safe in assuming that 2.910 is a good starting point ?

    • Sam
      Sam Millard
      February 9, 2018 at 12:29

      I usually look for a few of the same measurements, but all that matters is consistency. An average would also work, so you could use 2.906 if you want to do it that way. It took me a few tries to get comfortable with the whole process, but now I have no problems with getting the same exact value over several measurements.

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