Does Chamfering Your Brass Effect Bullet Seating Force – AMP Press Test

Lately we’ve been seeing the AMP Press used for tight quality control from precision reloaders around the world. While you’ve seen our tests on the AMP Press before, in this story, we single out 1 variable: Chamfering Case Mouths.


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About the AMP Press

From our AMP Press Overview Story:

From the AMP Press Product Page:

The AMP Press combines a motor driven ram, a distance sensor, and a load cell to deliver extremely accurate and precise Force / Distance bullet seating measurements. It is designed for use with inline bullet seating dies. For the first time, this data can be stored and sorted according to a multitude of variables. This allows users to enhance their case preparation, so as to achieve more consistent “neck tension”. It also allows users to batch their loads accordingly. Users can create cartridge profiles and store sessions for each caliber. Current bullet seating sessions can be compared to previous ones to accurately see how loads are changing (if at all) over time. The  picture below shows traces generated when seating bullets into ten virgin 308 cases. In this example, the lack of chamfering is quite distinct at the start of the trace. Considerable force is required to start the bullet entering the case mouth. Also visible is when the bottom of the bullet seats beyond the sized portion of the neck. This is indicated by the slight drop in force at the -0.16″ mark on the X axis. The seating force then levels out  until the bullet is fully seated. The last two traces (the red and blue one together) distinctly show two possible “flier” loads which could be separated from the batch.
    • Load cell: AMP Press comes equipped with a precision load cell which delivers exact weight measurements up to 200 kilograms. The face of the load cell is surrounded by a retainer which guides the die to the center of the cell. This ensures repeatable measurements every time. The load cell is highly accurate. Minute case to case variations can be magnified and displayed in incredible detail. The load cell face is free floating. This ensures that no binding takes place when the ram presses the die down onto load cell and that everything remains centered.
    • 12V Motor: The ram on AMP Press is driven by a high torque, DC motor. This ensures that a repeatable stroke in both speed and force is applied to the die when seating. This removes the human error which occurs when operating conventional arbor presses. The 12V DC motor means the press can be easily powered by batteries. This allows its use in more remote locations such as at a range.
    • Distance sensor: The position of the ram is calculated using a position sensor, which is accurate to 0.001″. This allows the distance to seat bullets to be displayed against force for the first time. This is especially useful in highlighting discrepancies such as trim length and chamfer consistency. It also allows for the calculation of “Total Work” to be applied to the plot as an option to sort by for the first time.
    • Bluetooth: AMP Press is Bluetooth capable allowing for wireless communication to your preferred device. Bluetooth will be enabled after the initial release of AMP Press. In the interim, computer connection will be by USB cable. Note: the initial release of AMP Press will be PC only. Mac software will follow.

Experiment Overview

The Amp Press takes force readings during bullet seating. What this allows us to do, is isolate specific characteristics and see how they effect bullet seating force. In this experiment, we’ve prepped every piece of brass the same way, with one variable – chamfering case mouths. We can take a look at our brass before chamfering, and see how much force is applied in order to seat the bullet. Then, we can take a look at our chamfered cases to see if chamfering helped with bullet seating force – either minimizing the force, or closing the gap in forces, giving our bullets a more consistent seat.

Preparing the Brass

We are starting with Brand New Lapua 6.5 creedmoor brass. Before beginning the experiment, we:

Conducting the Experiment

Now that we’ve prepped our Brass, we’re ready to start seating bullets. Here, we are loading for a reliable well-known load so we are using Berger’s 140 grain Hybrid Bullets. Let’s take a look at our first test group, non chamfered cases.

Not Chamfered

We seated 10 bullets into non chamfered Lapua 6.5 Creedmoor brass. This became our base line for seating pressures. Now that we have our control group, it’s time to take a look at what our seating pressures do after chamfering the case neck.


We seated 10 bullets into 10 chamfered Lapua 6.5 Creedmoor brass. As we watched the graph, we noted a few outliers. Besides these outliers, we noticed the seating forces did not deviate from the control group!

The Results, and Conclusion

To my surprise, there was little to no difference between the cases that were not chamfered and the cases that were chamfered. This is in stark contrast to a previous experiment which is summarized below. At the end of the day, the numbers do the talking. Chamfering has been a life long personal comfort when it comes to reloading. While I will continue to chamfer my brass just for peace of mind, the real story behind the data shows that bullet seating forces are not changed by chamfering.

Different Results from Previous Experiment

The last time we tried Chamfering the case mouths with the AMP Press, the difference between cases with and without case mouth chamfering were much more drastic: (most likely due to the fact that military 308 brass was used)

308 Test 1, Baseline: Full Length Sizing + Mandrel Neck Expansion

Brass was spray lubed, full length sized and then mandrel sized with a Wilson Mandrel die. Brass was then tumbled in walnut media to remove the lube. This is important to note as media dust residue will have an effect on the seating forces.

Results from Baseline (click/tap to enlarge):

This graph result showed what we expected. The initial spike in force was seen as the bullet started movement and ented the neck. This is followed by a dip and then progressive increase which is typical for the bullet seating process.

308 Test 2, Baseline + Inside Neck Chamfer

We added an inside neck chamfer using the Lyman Case Prep Xpress.

Results from the Inside Neck Chamfer (click/tap to enlarge):

You can see based on the differences observed in the 308 Winchester graphs that chamfering made a big difference in bullet seating forces. And that’s quite different compared to what we saw with the 6.5 Creedmoor cases!

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Travis Fox

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