5 Steps to “Pressure-Proofing” Handloads

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Here’s a few ideas on how to proceed in load testing to find the safe maximum velocity, and keep it safe…

We’ve chosen the sometimes twisting path to becoming handloaders because we want to improve on-target results. The difference between a handloader and a reloader? My wise-crack answer, which is honest, is that handloaders start off with new brass… We’re not about to shoot factory ammo.

Part of the process of developing the load we’re seeking is learning how to safely set a cap on its pressure. Most of us don’t have pressure-testing equipment, so we rely on measurements and observation to know when we’re at the limit. The goal often, all other things being the same, is to find the highest velocity we can get. Less drift and drop, shorter time of flight, all good. However! Knowing that the maximum tested velocity is also going to be safe over the long haul is a much narrower line to walk.

There’s not room here to cover every pressure check, all the symptoms that can point out over-pressure ammo, but I’ll share my two leading indicators: primer pockets and velocities.

  1. Always start load development with new brass! There are a few reasons, but the leading one related to this material is that the primer pockets will be at their smallest. So. Fire the cases, size the cases, and seat new primers. It takes a little experience, which means a few times through this process, but my leading indicator of pressure is how easily the primers seat. They’ll go in easier than on the first use, but if there is much less to very little resistance felt the second time around, that load is over-pressure. Period. The case head has expanded (I put a max of 0.0005 on expansion, when it’s measured with a micrometer). The more you use the same cases and repeat this process, the sooner you’ll get a handle on the feel to know when the primer pocket has overly expanded.
seating primer to check pressure
My primary gauge for pressure is primer seating — how easily a new primer seats into a once-fired case. This is an indication of case head expansion. It won’t be as tight as new, but it should still be snug. A low-leverage tool, like this Forster Co-Ax, increases the feel and feedback of this operation.
  1. Jump back, don’t step back. If you encounter a pressure symptom, come off a “whole” half-grain. Not a tenth or two. And if you see it again, come off another half-grain. Folks, if anyone thinks the difference between over-pressure and safe-pressure is 0.10-grain, that same little bit exists in the difference in 20-degrees ambient temperature with many propellants. Don’t cut it that close. Keep the long-haul in mind.
  1. Select a temperature-insensitive propellant (related to the above). There will be one out there you’ll like. I use a single-base extruded (stick) propellant when loading for the season. The propellants I choose are coated to help reduce temperature-induced changes. That season is going to span a 50+-degree range, and I don’t want August (or October) to force me back to the loading room… Temperature sensitivity works “both” ways, by the way… Hot or cold can induce pressure increases.
  1. Read the speed on each and every round tested. Beforehand, I have to assume you’ve gotten an idea in mind of what you’re looking to get for a muzzle velocity. If not, do that… A journey of this nature has to have a destination. If not you won’t know when you get there. If you are reading velocities more than 40-50 feet per second over a published maximum, that’s a flag. That 40-50 fps is usually about a half-grain of most propellants in most small- to medium-capacity cases. Certainly, there are all manner of reasons some combinations can vary, but, despite what your mother might have told you, you are really not THAT special…
  1. Don’t assume anything. If you have one round out of many that “suddenly” exhibits pressure symptoms, don’t guess that it’s just a fluke. It’s not a fluke. You finally saw it. Overwhelming chances are that the load is over-pressure and has been over pressure, and the question is how much for how long? Back it off. (The way you know it might have been a fluke, and that happens, is again based on how close to a velocity ceiling it is: if it’s a real mid-range velocity load, it might have been a fluke.)
primer indicators for over-pressure ammo
Some over-pressure indications are pretty clear. Left to right: new, nice and safe (notice there’s still a radius on the primer edge), cratered and flat, yikes! It’s another article, but not all piercings are caused solely by high-pressure ammo; an overly large firing pin hole size in an AR15 bolt contributes.

One last about primer appearances. Usually the first thing a handloader will do after firing a round is look at the primer. I do. No doubt, if the primer is flattened, cratered, pitted, or pierced that’s a honking red flag, and the immediate response is, you guessed it, come off a “whole” half-grain. However. Small rifle primers (especially some primers in some cartridges) do not exhibit the common over-pressure appearances. They can look just fine and shiny until they blow slap out. If you ever see anything that looks like a pressure symptom, back it off; however, don’t assume a load can’t be running hot if the primers don’t show it.

over pressure ammo, primer appearance
Here’s what I mean about primer surface indications not always revealing high pressure. The middle one is an incredibly over-pressure load fired through one of my AR15 race-guns with an extra-heavy bolt carrier. Primer looks just fine. Right hand case is what happened without the extra weight. Neither case would hold a primer after this one firing.

Back to the start: primer seating and velocity are the leading indicators.


The preceding contains specially-adapted excerpts from the new book “Top-Grade Ammo” by Glen Zediker and Zediker Publishing. See it by visiting ZedikerPublishing.com.

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7 thoughts on “5 Steps to “Pressure-Proofing” Handloads”

  1. I didn’t start with never fired brass. So expensive. But they were factory loaded ammo, and I did separate them by brand, also weighed them and did batches of reduced, medium, and hot loads. Used a magic marker colors such as green, blue, and black on the head stamp to indicate the load levels. 7mm with 139 grain soft points, and 150 grain ballistic tip bullets for hunting rounds. They all fired nice and accurate at about 1/2 inch spreads at 100 yards from a bench. 63 grains of powder,64, and 65.5 grains just rock! Used a Savage 111.
    I also hand load .357 Sig rounds, which I find challenging to say the least! Have destroyed the bottleneck so many times and they would budge just enough that they would not lock “battery” in my Glock 32. So, and I have read several blogs that say not to, but I resize .40S&W to .357 size and they actually work great as far as locking the chamber tight. I saw nothing adverse when looking at the fired brass. Using 115 grain hollow point Hornady bullets and 6.3 grains of powder( if I remember correctly) I don’t have a chronometer, but just a guess of around 1500 maybe 1600 feet per second velocity and very accurate at 15 yards. Am happy to read everyone’s loading tips and experiments and especially advice! As they say:Lock and Load. Thanks for the great articles.

  2. Glen I have just started loading my own 223 ammo, l have been loading for 33 years and all I appreciate your ariticles on them. This a/r with differents barrel twists and lengths can make you do a lot research on them to get the best groups. all Factory ammo don’t shoot the same in all weapons if think I am crazy try it and see.

  3. I have been shooting a 7mm Mag rifle for over 20 years. The load I shoot is in the middle of the list on powder, but it shoots faster than the highest listed load. You should of mentioned that you need to know what length of barrel the loads were tested at because longer barrels usually means faster velocity. Am still using some of the brass I started with and it is still good.

  4. Glen Zediker thanks for the heads up. Ive read that high pressure could not be read that way. But you are right 100 percent. For some time ive watched the signs of over pressure by also looking at the primers. Keep the articles coming there is always something new to learn. Over pressure can get you into trouble fast.

  5. I’m a neophyte to shooting….just got interested in long range shooting when I moved to wonderful Texas. I am interested in doing my own reloading and try to read or view as much info on this subject, hence my reading this article……thanks by the way..
    As a new born babe, I depend on advise and guidance from those much more experienced and with that in mind, ask where is a good place to start learning this wonderful skill?
    I’m using Midsouth Shooters as my go to site for info on equipment and articles from now on…..thanks for any help/guidance you can provide and PLEASE keep up with these educational pieces.

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