Reloading Step 2: Seating the Primer
Updated: Dec 4, 2022
This is the third installment of the multipart Blog all about rifle reloading. In this blog, I will explain a few items to check when seating the primer. Organizing the reloading process this way will allow for shorter reads and make it easier to find answers to questions you may have.
My top two rules while reloading:
# 1 Rule = Safety
# 2 Rule = Everything should be repeatable
1. Resize Case 2. Seat Primer 3. Add Powder 4. Seat Bullet
Safety Notice: When performing any reloading operation read and understand the manufacturer’s directions.
There is no need to complicate this. Seating a primer is…well...seating a primer. However, there are a few key items that deserve our attention.
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Primer Seating Depth
In the tuning puzzle, there are much bigger pieces than the seating depth of the primer. Nonetheless, depth is still a piece so we might as well do it right. A group of highly accomplished Benchrest shooters from Texas did extensive testing on the depth of primer seating. To make a long story short, they found that .002" - .004” was the ideal depth range.
To measure the primer seating depth use the depth indicator on the back end of the calipers. With the jaws shut (0.000) rest the beam on the case head. Slowly open the jaws (this will push the depth indicator to the primer) until the beam comes off the case. Gently push the calipers down until the beam is again flush with the case head. Read the measurement on the calipers. Average several trials to get an accurate primer seating depth.
I doubt I am a good enough shooter to be able to tell the difference between .003” and .005” primer seating depth in my bench rifles. I know I am not going to be able to tell that difference hunting when the wind is blowing fifteen miles/hour. All the same, if the experts say the ideal depth is .002" - .004", then we might as well go for it.
To change the depth of the primer pocket you will need a primer pocket uniforming tool. I use this tool on all my competition brass. I do not use it on my hunting brass unless the primers seat above flush.
I might not be able to tell the difference between .003 and .005”, but I can tell the difference if the primer is seated above flush. This is a bad situation. The bolt face is in contact with the primer instead of the case head. This is not only a safety issue, but also throws off any measurements taken off of the case head. (shoulder bump, base to ogive length, cartridge overall length, etc.)
Experience Tip: A good habit to get into is to check the depth of primer seating by feel. Simply rub the thumb over the seated primer. It will be very easy to tell if your primer is above flush.
A way to visually show if the primer is set too high is to put the primed case in the calipers and hold up to a light. A gap between the jaws of the caliper and the case head indicates the primer is above flush.
I have a couple different primer seaters. No matter which seater I am using, I like to feel a very slight crush on the primer. This ensures that the primer is seated firmly against the primer pocket.
At home, I use the Lee Auto Prime on a dedicated press. It is fast and gives a decent feel for the depth of seating.
At tournaments, I use a K&M primer seater tool. It gives excellent feel and is shaped for all day use with no hand cramping.
There could be a burr left on the inside of the case from the factory making the flash hole. I like to check all my brass (hunting & competition) by using a flash hole deburring tool. This is a quick procedure and only needs to be done once in the lifetime of the case.
Forgot to Seat the Primer
If you add powder then realize you forget to seat the primer, (Yes, this happens more often than you think, especially for those who load at tournaments) do not try and add the primer later. There are two main reasons for this: Obviously safety is number one. You are playing (literally) with fire. The risks greatly outweigh the rewards. Second, there is a high probability your powder charge will be inaccurate. Powder kernels can fall through the flash hole and out the primer pocket.
Primer Pocket Expansion
If you notice the primer feels loose in the pocket, that could be a sign your load is too hot. Double check your load in a reloading manual and check for other pressure signs.
Some common (but not all) pressure signs
* Cratered primers
* Pierced primers
* Loose primers (primer pocket expansion)
* Ejector groove marks
* Hard bolt lift
* Sticky case extraction
* Pressure Ring on case
Follow all safety protocols and make sure the primer is seated slightly below flush. Follow those two rules and you will quickly be on your way to the next step in the reloading process. Until next time, enjoy the experience.