Reloading 101: Determining Safe Maximum Velocity

By Glen Zediker published on in Ammunition, How To, Reloading

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 with new brass… We’re not about to shoot factory ammo.

Pressure gauge for primer seating

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.

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

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—other things being the same—is to find the highest velocity we can get. Less drift and drop, shorter time of flight—both are 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 or all the symptoms that can point to 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 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 they did on the first use. However, 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.

    Four cartridge heads showing the effect of pressure

    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.

  2. 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.
  3. 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. Hot or cold can induce pressure increases.
  4. 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…

    primer indicators for over-pressure ammo

    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.

  5. 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. Te overwhelming chances are that the load is over-pressure and has been over pressure, and the question is how much and 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.)

One last thing 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. The immediate response is, you guessed it, come off a “whole” half-grain. However, small rifle primers do not exhibit the common over-pressure appearances. They can look just fine and shiny until they blow out. If you ever see anything that looks like a pressure symptom, back it off. But, don’t assume a load can’t be running hot if the primers don’t show it.

Parting Shot

Primer seating and velocity are the leading indicators.

Are you a reloader or a hand loader? Do you have an over tip or story? Share it in the comment section.


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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Comments (13)

  • Deplorable Robert

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    I truly enjoy hand loading. I shoot 7 mm. Remington Mag and load for 139 grain and 150 grain Hornady bullets. I always weight my cases after ensuring they are all overall case lengths are all identical. After grouping them in 20 case lots, I load them all with one set loading charge. Most are lighter loads, then the heavier cases get a 150 grain ballistic tip with an. Extra one or two grain of powder, which really shoots great in my Savage rifle. Can usually keep it in a half dollar at 100 yards using a rest and a cheap scope. Nothing fancy, but pretty accurate enough to get ‘er done.
    My .357 Sig is a little more temperamental. Hard not to crush the shoulders. And I have used.40 S&W cases resized and they really shoot nice in my Glock32. Next step is to purchase a quality chronograph and check my “light” loads in 115 grain hollow points, and keep it around 1400fps and check accuracy AND velosities. Maximum Velosities I guess! 😎

    Reply

    • Deplorable Robert

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      Weigh my cases…..sorry, wish they had an edit button 😎

      Reply

  • Wireslinger

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    In 1969 Mike and I roamed every intersection of our small town looking for wheel weights to cast bullets. We could not afford to load anywhere near maximum. Now that I am a lot older, I have experimented with near maximum loads in handguns and rifles. Several of the competition shooters I have met all agree maximum loads affect accuracy, and I agree. Please follow whatever manual you have, I use Speer and Lee manuals, and never exceed maximum. Also, here is a hint, weigh your brass. Brass from the same manufacturer and lot will vary. Heavier weight means less volume. This is of course if you are interested in putting round after round through the same hole. I am happy with a one inch group. Be safe.

    Reply

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