The old link to this set of Instructions is no longer working. So, I'm re-entering the Instructions for those of you who want to try CHE & PRE to determine if your Loads are at a Pressure similar to Factory Loads.

Case Expansion Measurements
Case Head Expansion and Pressure Ring Expansion


Liability Disclaimer: Anyone taking Pressure Expansion Measurements following these directions do so at their own risk. I have used these methods SAFELY for over 5 decades, but I can not be held responsible for anyone misreading their Micrometers or in how they choose to use the results.


When using these methods with "Straight Wall" style cases (9mm, 357Mag, 444Mar, 45-70, etc.) you must use Full Length Resizing(FLR). Partial Full Length Resizing(P-FLR) does not apply to this style case.

When using "Bottle Neck" style cases (223Rem, 308Win, 30-06, 7mmRemMag, 375H&H, etc.) I encourage the use of the P-FLR method throughout the Load Development. If you will be near Dangerous Game during your hunting, then always Full Length Resize the cases you will be using for the Hunt.


Items Needed

1. A box of Factory ammunition.
2. An appropriate firearm.
3. A 0.0001" capable set of standard Micrometers. (Note: 0.001" capable Calipers are just not accurate enough for taking these measurements.)
4. A 0.0001" capable set of "Thin Blade" Micrometers. (Only necessary for non-belted Case Head measuring.)
5. A Load Data Sheet.


General Summary

1. Fire a Factory round.
2. Measure the "widest diameter" across the Pressure Ring with 0.0001" capable Micrometers.
3. Record this value as the Pressure Ring Expansion(PRE) on a Load Data Sheet
4. Calculate the PRE Average for the entire box of cartridges.
5. Record the PRE Average on the Load Data Sheet and on the box the cartridges came in.
6. This establishes the "Factory Standard Pressure Value" for this specific Lot of cases. This PRE Average will be used as the MAX Pressure Ring Expansion acceptable during Load Development.
7. Make a note that the cases have been "Fired 1 time" on the Load Data Sheet and the box.
8. Reload this Lot of cases with your first "Test Loads.
9. Before firing, measure across the Case Head in one specific spot and record this value on "a new" Load Data Sheet.
10. After firing, re-measure the Case Head in the exact same spot and record.
11. Subtract the "before firing" dimension from the "after firing" dimension and record as the Case Head Expansion(CHE).
12. Also after firing, measure the PRE and record.
13. Repeat both CHE & PRE measurements for all Test Loads.
a. When Case Head Expansion reaches 0.0005"<->0.0007" on your reloads, STOP.
b. When Pressure Ring Expansion reaches the same value as the "Factory Standard Pressure Value", STOP.
14. If neither value in #13 is reached, note "Fired 2 times" on the Load Data Sheet and the box, and reload the cases with an incremental increase in the Powder. You must use the same Lot of Primers, the same Lot of Powder, the same Lot of Bullets and the same Bullet Seating Depth.
15. Continue the Testing until a 0.0005"<->0.0007" Case Head Expansion is attained or the "Factory Standard Pressure Value" is duplicated.
16. You have now created a SAFE MAX Load for this Lot of cases.
17. This Load can be SAFELY duplicated in Lots from the same manufacturer where the weight of those cases is the same or less.
18. This SAFE MAX Load is for this one specific firearm ONLY!
19. Changing to a "New Lot" of any component used in the Load requires that you re-verify the CHE & PRE.


Details and Explanations

Case Head Expansion(CHE) can be "tricky" to read for a Beginner. So can properly setting up a Sizing Die, determining the proper bullet Seating Depth or getting a Home Strain Gauge System(HSGS) like an Oehler M43 or Pressure Trace System properly attached to the chamber. With practice, and knowing how many shots have been through your cases, you can determine when to STOP increasing the Powder in your Load resulting in a SAFE MAX Load. This method will tell you for sure when you have reached an Un-SAFE Pressure. Yet, CHE is NOT AS RELIABLE an indicator as Pressure Ring Expansion(PRE). PRE is fairly straight forward and easier to quickly get a grasp on.

When taking the CHE & PRE measurements, you will use the Micrometer slightly different in order to obtain the most accurate values. When measuring CHE, you will use the ratchet feature on top of the Micrometer spindle to determine when the anvils are at the correct tension against the case head. When measuring PRE, you will set the Micrometers "just tight enough on the case to keep it from falling out from between the anvils".

You measure CHE in one specific spot on the Case Head. CHE measurements must be taken before and after firing. Align the Micrometer Anvils with one of the numbers or letters found stamped into the case head. Turn the "ratchet" until it slips and read the Micrometer. Record that value for the "before firing" Case Head measurement on the Data Sheet. Lets say you measured 0.4121". (Note: The numbers used throughout this paper are all fictional.) Fire the round and remeasure the case head in the same exact spot. Lets say you measured 0.4125". Record the "after firing" measurement on the Data Sheet. The difference between the two measurements is the CHE. Subtract 0.4121" from 0.4125" and your CHE is 0.0004".

When measuring PRE, you will be rotating the Pressure Ring on the case inside the Micrometer Anvils to locate the "widest diameter". You must be careful not to deform the Pressure Ring by "forcing" it to turn between the anvils. Once you locate a tight spot, open the micrometers slightly and turn the case until you locate the "widest diameter". For an example, lets say you get a measurement of 0.4772" at the widest diameter. Loosen the Micrometer to 0.4773" and see if the widest diameter on the Pressure Ring will "hang" between the anvils. If it won't hang, record 0.4772" as your PRE measurement. You only measure PRE after the round has been fired and record that value. Loosening and tightening of the Micrometers does take a small bit of time to make sure you are recording a repeatable value. But, it goes real fast once you get used to it.

1. On Belted cases (7mmMag, 375H&H, etc.), CHE is measured across the Belt.
2. On Non-Belted cases (223Rem, 7mm-08, 30-06, etc.), CHE is measured just forward of the extraction groove (where the Belt would normally be located) with special "Thin Blade" Micrometers.
3. On Straight Wall cases (9mm, 357Mag, 444Mar, 45-70, etc.), CHE is measure just forward of the Rim with special "Thin Blade" Micrometers.
4. On a "fired" Belted case, PRE is measured across the "widest diameter" of the case body forward of the Belt.
5. On a "fired" Non-Belted case, PRE is measured across the widest diameter on the case body forward of the Extractor Groove.
6. On a "fired" Straight Wall case, PRE is measured across the widest diameter on the case body forward of the Rim.

The Pressure Ring is located in the same spot on the case body where Case Head Separations occur. If you have a Speer #12 Manual, look on page 72 and it is where the cases have split in the bottom two pictures.

In order to measure PRE, you will need to either P-FLR or FLR Bottle Neck style cases and FLR Straight Wall style cases between shots. Neck Sizing will not reform the case wall properly for these measurements. Once you know where the SAFE MAX Load level is located, then you can go to Neck Sizing if you so desire.

Adjusting a FLR Die to P-FLR is done by "slightly raising" the FLR Die higher in the press than normal. When adjusted to P-FLR properly, the bolt closes on an empty, length-trimmed case, with a slight bit of resistance. This indicates you have a crush fit between the case-head/case-shoulder and the bolt-face/chamber-shoulder. That ensures the longest possible case life, helps prevent case-head separations and increases the accuracy potential of your rifle/load combination. This is also referred to as "Zero Headspace".

CHE measurements vary considerably on the very first firing of a new case. This is why you do not bother to measure them on the initial firing of the Factory rounds. If you desire to see the variance, just measure the factory rounds on the initial first firing. I do not recommend this for novice reloaders since it will create confusion for you as to why that is so. CHE measurements become more reliable for firings 2-5. Then CHE measurements become somewhat unreliable after 5-7 firings, depending on the strength of the previous Test Loads. This is due to "work-hardening" of the brass in the case head.

If you are using a Non-Belted or Straight Wall case, you will need to buy a set of "Thin Blade" Micrometers to measure CHE and the Thin Blade Micrometers can be expensive, $160 or so. But, I found a nice used set in a Pawn Shop that was asking $50. I got them for $25. On a Belted case you can measure CHE with regular $35-$45 Standard Anvil Micrometers.

PRE is measured using regular 0.0001" capable Micrometers whether the case is Belted, Non-Belted or Straight Wall. PRE measurements can be taken on the same cases 7-10 times, depending on the strength of the previous Test Loads. PRE is useable on ALL firearm cases and is the best method of the two. I encourage the use of both CHE & PRE so you end up with an additional set of Pressure Indicators, but a person can get by with PRE alone.

The Micrometers must be 0.0001" capable in order to be accurate enough for all of these measurements. A 0.001" capable Caliper is just not accurate enough and will mislead you if you try to use them, making all your Expansion Measurement data worthless and dangerous.


An Example and some Questions

Here is an example and some questions I've answered in the past. The questions came from other folks I've taught these same methods to. The questions are answered as if the person reading this has "no experience" with these methods at all. If I was responding to someone who has had experience with these methods, some answers would be slightly different.

None of the Expansion Values listed below relate to a "Standard Factory Made Case". This is because cases vary from Lot-to-Lot and Manufacturer-to-Manufacturer and any values listed from "my" cases would be misleading to you. However, I will give some Expansion Values in this discussion. Just understand they are made-up fake-data and used for "Example Only". For this discussion, we will be using the mythical "BOGUS" cartridge (aka "Big Ole Good UnS-44DD". Fun to handle, fun to play with and really gets your attention when FULLY Loaded.

1)How can you be sure what your pressures are at if you have no instrumentation like an Oehler M43 or Pressure Trace (Home Strain Gauge System(HSGS)) to validate it?

Answer: If you measure the PRE of the factory-loaded BOGUS cases after their initial firing, you might find PRE values of 0.5158", 0.5154", 0.5159", etc. across the entire Lot. This could result in a "PRE Average" on the factory BOGUS cases of 0.5157". This 0.5157" PRE Average is what you will eventually use as your indicator that your particular cartridge/load/rifle has reached a SAFE MAX Pressure. It should be thought of as the "Factory Standard Pressure Value" for the Loads you will be developing.

You make your first (low-level, non-max) BOGUS reloads, using 200.0gr powder in 3 of those cases. These cases might "typically" give CHE values of 0.0000", 0.0002", and 0.0001" or a CHE Average of 0.0001". The PRE Average on the same cases is 0.5134". So, both the CHE Average and the PRE Average values indicate you can "SAFELY" increase the Load.

(NOTE: The actual increase in powder for the next firing depends on how far away from the SAFE MAX Load you are, the size of the case you are using and the type of Powder. You might have to raise the load 2.0gr-10.0gr(in a real rifle cartridge) before you see any CHE increases of 0.0005"-0.0007" from your initial set of reloads. Always start "low" and develop your Load from there. You may be able to go "up", or you may need to go "down". Of course, you really have no way of knowing what CHE & PRE will be, until you fire some loads and measure them.)

Our second set of 3 Test Loads for the BOGUS cartridge increase the powder to 200.5gr (using the same Lots of Primers, Powder, Bullets and the same Bullet Seating Depth) you may see the typical "range" of CHE on 3 cases read 0.0003", 0.0004" and 0.0002" or a 0.0003" CHE Average. Yes, the numbers "vary" and you have to watch for a "trend" as opposed to the "exact same CHE increase" on each case. (Same situation when using the HSGS.) Your CHE values are still well below 0.0005"<->0.0007" Expansion. And lets say the PRE Average was 0.5146" for this Load which is still below the 0.5157" "Factory Standard Pressure Value".

The third set of 3 Test Loads raise the BOGUS load to 201.0gr. As you reach a 0.0005" CHE Average and a 0.5157" PRE Average, you have reached the SAFE MAX Load as far as the Factory was concerned for that Lot of cases. There is a chance you could see CHE vary up to around 0.0007"<->0.0009", but that is not as good a Pressure indicator as the PRE. Only experience will give you more confidence in the CHE values.

If you do get a Case that shows 0.0005"<->0.0007" CHE be sure to watch for Loose Primer Pockets. If that happens, then the 0.0005"<->0.0007" CHE is just too much Pressure and the Load will need to be reduced. You should easily get 10 reloads in a Case and still have snug Primer Pockets, if not, back the Load down a bit. A 100-200fps increase in Velocity is not worth short Case life and exposing your firearm to High Pressure which can result in Cumulative Metal Fatigue.

2)Soft brass will show more expansion and do so sooner than hard brass will. Wouldn't you then have lower pressures?

Answer: ABSOLUTELY, POSITIVELY YES!!! (It you get nothing else out of this discussion, let that sink in.) And that is what you want to happen. Here is the "Achilles' Heel" of the HSGS, it CAN'T tell you if the case is soft. If you use the HSGS "alone" to determine a SAFE MAX Load, you can have too much Pressure and end up with reduced case life and potential Case Separations due to over-loads. But would it be Un-Safe? Probably not today, because the cases we have available right now, are much more consistent than they were 20 or even 10 years ago. But, it is always best to get Pressure information directly from the case itself. And having to trash cases after the 3rd firing is no good at all.

One real "key" to understanding CHE & PRE is, "it just DOESN'T MATTER what the numerical Pressure value in CUP or PSI actually is". You are comparing your Load, to the "Expansion"(Pressure) the Factory deemed as a SAFE MAX (your "Factory Standard Pressure Value") for that Lot of Factory loaded BOGUS cases.

2A) Now, is this Load "below" what a person will decide is SAFE using the HSGS?

Answer: Maybe, then again maybe not. But it doesn't matter, because the Factory folks have entire Quality Departments dedicated to "continual-testing" with their Millions of Dollars of Labs and Test Equipment to ensure that the ammunition they make is SAFE. We are just using what the factory determined was a SAFE MAX for that Lot of cases to establish our "Factory Standard Pressure Value".

Once you know what a SAFE MAX Load is for your firearm using specific "Lots" of components, then you can compare your previous CHE & PRE measurements, to Loads made in "new virgin" cases to develop SAFE MAX Loads for them as well. But, it will take a bit of time to become familiar with these procedures. Just go slow and have patience.

3)On the other hand, hard brass that shows little expansion would require higher pressures to show expansion. Wouldn't you then you be over the maximum pressures?

Answer: No! Since you will be using the Data you measured from the factory BOGUS cartridges as your "Factory Standard Pressure Value", that is automatically compensated for.

Lets use an example of bending a 6ga wire back-and-forth (work hardening it) in order to break it off. Depending on the alloy composition of the wire, diameter(thickness) and temper(hardness), 8-10 flexes may only serve to reduce its strength slightly, warm the point of flexure, thin the point of flexure, but still retain most of it's original strength. On the other hand, a different composition and temper might just snap after 3-5 flexes.

So, how does that apply to the BOGUS cases? Depending upon the alloy composition, thickness (of the case wall) and hardness, coupled with the strength of the Load, the case will expand and contract (flex) in different amounts. In order to be sure about what is going on "with-the-case" you need to "measure-the-case" not the rifle's chamber. That is why it is nice to be able to measure the CHE & PRE from the case you are developing your Loads in. And real nice that you can compare the PRE with the "Factory Standard Pressure Value".


Bob Hagel and Ken Waters, gun magazine writers and authors of many reloading books, use CHE & PRE extensively during their Load Development. If there are two more competent reloaders than them, I just don't know who they would be.

Finally, NO ONE needs a HSGS or a chronograph to be able to develop SAFE MAX Loads. If however a reloader has access to a chronograph, he should use it as "one more source" of information concerning his loads. Always use ALL means available that provide relative information concerning your Loads and record that information for future reference.

If you know anyone else this document would help, feel free to pass it on to them.

Good SAFE MAX performance Loads to you.

Hey HC, you fishing?

Throwing your bait out and hoping to catch a Gibson fish? I think you cleaned out all the Denton fishes a long time ago!

Naw, the old Link went dead and I have folks asking how to do it. Rather than put the same Instructions out everytime and use up bandwidth, a Link to it works real well.