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 (11)

  • Elton P. Green

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    I’ve been reloading since I was about 15. I’m 65 now. I have reloaded .223, 243, 6mm Remington, 25-06, .308/7.62X51 Nato, 30-06, .300 Winchester Magnum, .270 Winchester, .35 Whelen, 45-70, 50-90 Sharps, .44 Special/Magnum, .357/.38, .45 ACP and others. I use Alliant, Hogden, IMR and Accurate powders. I use a spectrum of bullet weights, according to intended use and accuracy. I learned early not to go for the maximum listed load. As to pressure signs, if you use velocity you need a baseline. Factory ammunition gives you that. I also measure the case head of brass, examine the primer, look at how far the brass is ejected in a semi automatic, look at the cartridge face for scuffing from the bolt and to see if there is any imprint from the bolt. I feel for bolt lift with bolt action rifles to determine if any binding is occurring. I check the primer for cratering and flattening. A good gage for this is factory ammo fired from the rifle being used. If your rifle is throwing your reloads farther than it does factory brass, if it is a bolt gun and the bolt takes more effort to open than it does with factory, or the primer is completely flat, or the face of the cartridge is being scuffed, imprinted or marred by the bolt face, your loads are too hot. Also, velocity is not that good an indicator. Factory loads are tested in a 24 inch test barrel. If your rifle barrel is 22 inches or 26 inches, the velocity won’t match factory specs. In some cases, such as the Short Magnums, the factory loads use special blends of powders which hand loaders can’t duplicate. So check the velocity of a factory load in your rifle and get a baseline. Then try to duplicate that load, not the factory figures. Also keep in mind that any change in any component in a load will change the pressure, accuracy and probably point of impact of your load. Don’t chase velocity. Go for a safe load which combines good to excellent accuracy with acceptable velocity. You will need a good chronograph, though.

    Reply

  • boss45

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    I typically reload but on occasion I will fireform new brass to load for accuracy. Mostly just to prove loads and compare Brass geometry after firing. I’ve found that even in the same lot of new cases there will usually be cases that show pressure signs sooner than the bulk of the lot. I separate these cases when I find them and work a load at lower pressure using the same powder if I can keep the load density above 80%, then load the lot accordingly. I generally try to find the optimum velocity for the bullet/barrel combination I’m working with and paying close to pressure signs. I have yet to find any two firearms to yield the same results with the same load. A safe load for one chamber may be too hot in another. I shoot for lower pressures if I can get my optimum velocity changing powder or primer or even seating depth if needed. Don’t usually worry about chamber yield pressures because the brass will fail first.

    Reply

  • Bill W Koenig

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    Kim,
    And all handloaders and reloaders.
    Kim makes several excellent points, and has the clear thoughts and checks all the right things. In Kim’s case of primers getting loose, and with 12 loadings on the brass, this is very likely NOT a case of too much pressure. It is simply a case of brass reaching the end of it’s serviceable life span. He knows his rifles, and he knows his limits. Some rifles can take a lot more pressure than others, and do it safely. Use a tough thick walled brass like Starline, and a good heavy chamber barrel, and pushing factory pressure limits although a risky thing to do, would not be a large risk. This is an OUTSTANDING reason to pay a lot more attentions to PRESSURE instead of VELOCITY. If the brass starts to flow into the extractor and ejector spring cavities, then BACK OFF.

    Reply

  • Bruce

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    I started reloading when I was 16 with a Lee reloader. If I had a dime for every case I have reloaded with that thing I could buy a small boat!
    I remember one evening I was in my bedroom reloading .30-06 cases on my desktop. I was priming a case when I het the priming rod just a tad too hard with my mallet, this caused the primer to go off and shot the priming rod out of the case and it bounced off the ceiling. The bang was so loud in my room that it caused my ears to ring for several hours after. It really was a wonder why a neighbor did not call the police because it was that loud.
    After that, I saved enough money to purchase a reloading press and to this day, have not had another expected BANG! Scared the wits out of me!

    Reply

  • Joseph Smith

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    Primer pocket growth almost always happens only when the pressure exceeds the yield strength of cartridge brass. That means that the implied focus is on those cartridges with a SAAMI Max pressure greater than about 55,0000 psi.

    There are a lot cartridges, even modern ones, with SAAMI max pressures that are less than this level. Hence, reading primer pocket size for these cartridges can be a dangerous practice.

    Reply

  • Kim Curtis

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    I was shooting my PTR 91 a week or so ago and when I picked up my brass I noticed that 2 of the cases had no primers.
    I have reloaded, yes I’m a RELOADER, for over 40 years and I am guilty of high pressure loadings on a frequent basis!
    I tossed those cases in the scrap bin and told my friend that I couldn’t use those any more because they had too many loadings on them! I had reloaded that lot 11 times from the original so, they had been loaded 12 times!
    I might add that I have never had a head separation in all those years!!
    I get the most out of my brass and then, rather than sell it for scrap, I will deprime the cases and melt them down for use as finger guards in some of my knife making projects!
    My standard load for 308 Winchester is 44 grains of IMR 4064, using CCI large rifle primers and Sierra 165 or 168 grain boat tails.
    Several of my older loading manuals show that one can, with those components, use as much as 46 grains of that powder! THAT IS really WAY overpressure!
    I assume that the differences are due to the way these powders are manufactured today, as opposed to the way they were, years ago! Also, the ingredients in the powders are more than likely more modern than the older powders!

    I have recently purchased a chronograph and will be testing my loads from here on out!
    Before anyone starts lecturing me on safety and all of that, I KNOW, my loads are somewhat overpressure! SO, don’t bother!
    I am using the finest heavy barreled rifles and if, as I suspect the chrono shows they are a lot over, I WILL back off.
    I really hate to have to do that as these handloads are extremely accurate in my rifles, all 2 of them! Usually less than half MOA at 100 yards! For a disabled hunter, like me, that’s usually better than I am! I used to be that steady, but, not any more!
    I do hope that those of you reading this post will realize that I am not recommending that anyone load overpressure loads! What I do, I do at my own risk and my own realization of what I am risking!

    Reply

  • WACATTACK

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    I agree with Koenig. Never heard of “Safe Maximum Velocity” except dealing with a bullet not being stable due weight, twist and speed.

    Other than the misleading title this was a good article.

    Reply

  • Spencer

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    I’ve been hand loading since 1968 & decided within a year that I’ll never load for anything but accuracy. Since then, I’ve never been concerned about velocity. If I sense more effort with bolt lift, I begin paying more attention. Since I’m a titewad, I prefer to stay away from maximum loads for only one reason. Maximum loads erode the barrel throat faster and premium barrels are expensive.
    I pay attention to primers & if I see any minute signs of cratering, I’ll try .5 grains more to see if it increases. If it does, I’ll drop back one full grain. to see if anything changes for the better. If it does, I consider that my maximum load.
    I always start midway between minimum & maximum. On any new powder or bullet combination. I also keep very detailed records of all my loads. I never chamber a round until I’m ready to shoot simply because a hot chamber can cause increased pressure if the cartridge is cooked for a while. Which I also believe can affect accuracy.
    I prefer a single shot rifle for that reason.

    Reply

  • Ammo Reloader

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    Awesome article as always.Just be careful if you decide to reload ammo because you need to know what you’re doing or else you can have a lot of problems.

    Reply

  • Bill W Koenig

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    I really hate that you titled your article as “MAXIMUM SAFE VELOCITY” That’s going to get someone in trouble. Let’s face it, the velocity is VERY dependent on the bullet shape, engagement surface area and other factors. PRESSURE is the both Jeckle and Hyde in one entity. A 100 grain bullet with 60K pressure will make 3,000+ fps easy with no over pressure. A 180gr bullet with the same powder charge will destroy a barrel and barely make 2400 fps. Choice of powder can be the devil where pressure is concerned. Pressure will do the damage or do the magic when one flies right. Please stress to those you talk to to get the specs on the firearm and KNOW what the maximum pressure rating is.
    No manufacturer publishes information on maximum velocity. No powder manufacturer publishes a maximum velocity. They will indicate what the anticipated velocity will be, but that is very dependent on bullet type, barrel condition and final reamed or worn bore dimensions. Most published loading tables state the pressures that will be anticipated with a load. Preach pressure, pressure, pressure. I have been hand loading for more decades than most people I shoot with have been alive and have seen loading mistakes of almost every flavor. I have never seen a firearm damaged by excessive velocity, but more than a few damaged by over pressure.

    Reply

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