Quick easy and dry

Alex Findlay - 29/07/2021


Sorting cases by volume using an AMP Press.


Hypothesis: That as cases vary in volume, the height of the powder column will also vary, and that this difference will be detectable on the X Axis of an AMP Press display.



·         AMP Press

·         Modified plunger to suit inline chamber seating die.

·         V3 auto trickler and A&D FZ-300i scale

·         7” powder drop tube

Proof of concept



The seating stem of a 308W inline seating die was modified so that it was able to extend into the case mouth. The extension was turned to 0.30”, again, to allow it to enter the case mouth.

Prototype extension mod shown in brass. A production version could be a caliber-specific single steel stem, turned to correct diameters.

We used one single 308W case for all tests. This case was charged, measured, emptied and re-charged with various weights of powder. After each charging, the case was inserted into the die and the modified stem was gently lowered to touch the top of the powder column. The die was adjusted to allow approx 0.10” of travel, depending on the charge, before bottoming out at the "find X zero” point.


We initially used Varget, using a funnel to tip each charge into the case. We got erratic results. Varget is a very coarse-grained powder. We also tested Hodgdon CFE 223, which is a very fine powder. It gave more consistent results, but it tended to stick to the bottom of the modified seating stem. We then used Benchmark ll, which is a relatively fine-grained stick powder. It gave promising results and did not stick. With charges coming up to the neck/shoulder junction, powder height changes were visible to the naked eye depending on how the charge was poured into the funnel. We then swapped to using a 7” drop tube, and instantly results became much more repeatable.


The following photo shows four different charge weights of Benchmark ll, using the drop tube:

The sloping trace from left to right was made using the spring-loaded simulation die. This gives a reference point for all the other traces. From the left, the first set of five traces shows 47.5 Gr. of Benchmark ll. The second set shows five traces of 47.0 Gr., the third set shows five x 46.5 Gr. and the right-hand set shows five x 46 Gr.



When the correct technique is used, a resolution of much better than 0.5 Gr. is achievable using the AMP Press to measure case volume. Resolution in this proof-of-concept test is actually better than 0.25 Gr. Note that this method of testing is only valid if powder charges are sufficiently accurate and uniform.

Because this test demonstrates that different charge weights show measurable powder column height variations in the same case, the corollary is that if multiple cases are charged with the same charge weight, any variation in charge height indicates variable case volume. This will allow for very accurate case sorting. Users could choose to either sort each new batch of cases as a one-time process, or possibly test each reload. That is feasible because the technique is quick, easy and dry.


Where to from here?


We believe that further testing will allow us to optimize our techniques. We have also yet to test other cartridges etc. If all goes well, we will add a new function to the AMP Press software which gives dedicated a "Sort by case Volume” window. This will make it easier to analyze results with a different auto-scale function. We will also produce die compatible steel plungers for the various calibers as accessories.