Seating Depths


Oct 24, 2004
Seating depths?

I notice that the Nosler manual gives no seating depths and only a maximum COL for every cartridge.

While trying to develop a better load for the 270 WSM I went back to using Sierra bullets to establish a base line. To be frank I usually seat bullet close to the lands and in that rifle the COL would be about 2.9" for many bullets. Since the rifles magazine will easily take a load 3.05" long it makes for maximum powder capacity and a nice looking round.

Since I was not getting very good accuracy I read the manual and the COL for the 140 gr SBT is suggested at 2.765" which is a lot less than what I had been loading your 140 gr Ballistic Tip to.

The short 2.765" seating depth for the Sierra 140 was the best in terms of accuracy. In fact now the rifle is shooting better than I can.

What is the suggested seating depth for the Nosler 140 gr BT's and Accubonds for that cartridge?
There is no one "best" COL for any cartridge. The best in one rifle is likely not going to work as well in another. The Sierra load that now shoots well for you is a good place to start looking for a COL with the BT and AccuBond bullets. I`d find the distance off the lands of the ogive- a Stoney Point or Sinclair tool helps- and seat the Nosler bullets to the same distance. The sweet spot for these bullets in your rifle should be very close to the same as the Sierra and a bit of adjustment from there should get you where you want to be.
Don`t be suprised if the COL of your BT load ends up ~0.10" longer then the Sierra. I`ve found in alot of cases the two are very different in shape and the BT might not fit your magazine when seated the same off the lands as the Sierra.
What seating depths does Nosler use to establish their loading data for each load?
That is a pretty good question.

Most times 99% of the time when developing loads we will use SAAMI OACL.

There are times we will seat the bullet as follows:

To determine the best seating depth for your individual gun you will need:

1. A cartridge case that has been fired in your gun, and not resized.

2. A bullet of the type to be used, with a full, undamaged nose.

3. Calipers.

4. A dark felt-tipped marker.

Step 1 Insert the bullet into the neck of the fired case. It should fall freely into the case, with no resistance.

Step 2 Remove the bullet from the fired case and press the case neck lightly on a flat surface to create a small indentation or flat surface in the case neck so that it will grip the bullet.

Step 3 With the marker, completely color the bullet.

Step 4 Insert the bullet, base first, into the case so that the case just grips the bullet by itself. Just get the bullet started into the case–don’t seat it too deeply.

Step 5 Gently insert the case and bullet into the chamber of the firearm, and close the action. Do not pull the trigger.

Step 6 Carefully open the action and gently remove the case.

Step 7 Retrieve the bullet. It will either be stuck up in the lands of the barrel or still in the case. If the bullet is stuck in the lands, it can be removed by tapping the butt of the gun on the ground. Or, it can be dislodged by gently pushing it out with a cleaning rod. If the bullet is still in the case, then gently remove it with your fingers, taking care not to mar the ink, and proceed to Step 8.

Step 8 During Step 5, the lands will have contacted the bullet and pushed it back into the case, causing the case neck to scrape the ink off of the bearing surface of the bullet. Simply push the bullet into the case until the edge of the case neck is just to where the ink has been scraped off.

Step 9 Carefully measure the overall length of the dummy cartridge. This overall length is called your “rifle seating” depth. It is where the bullet contacts the lands of the barrel. This length is different for every different type of bullet, as it depends upon the shape of the ogive (the taper) and the meplat (the tip of the nose) of the bullet. This process should be repeated three or four times to obtain a consistent average.

Step 10 Set your seating die to seat at a depth between .015 and .030 inches less than your rifle seating depth (this is generally where the best accuracy is found), and check to see if the cartridges will function through the magazine at this length.
I've tried this method in one of my rifles but the result is the length of the cartridge is much too big for my action. I can't even eject it with the bolt using this method. So I end up seating the bullet far enough back to fit in my action. But that puts me pretty far back from the lands. Anyone else had this problem?

Keep in mind, I am relatively new to hand loading so I could be missing something obvious.
Rattlesnaker, This is pretty much a common problem, especially with some bullet shapes. Rifle throats are not always short enought to allow seating to the lands either, again not uncommon. The bench shooters seat to the lands as much to insure the tension on the bullet is the same for each round then as a "sweet spot" in their barrel. To them even ignition is as important as the bullets seating point and a well built rifle with even barrel harmonics will toss the bullet to the same place as long as it starts from the same spot.
Don`t worry too much about it though. The idea is to seat the bullet to the point that it exits at a static spot in the barrels vibration. This isn`t a point only at a specific distance from the rifling but can exist at multiple points forward or back from the origin of the leade. Try differing the COL of your cartridge and watch for improvments in accuracy. You should find a second spot that works at some point deeper then the first one off the leade. How much deeper one can`t say but it shouldn`t be more then around 0.10-0.15", then again it might be right where you are. Just work back in increments until you find one or geometery of the bullet hinders deeper seating . The old Swede mausers and Weatherbys have very long throats and both are noted for their fine accuracy so it can be done.