Pressure: when is too much and why?

[Mike D Texas]

I can only speak to what I do and what works for me in my rifles.

I do a pressure test “ladder” for every cartridge, powder, bullet combination I shoot. I, like Jake push things to the max. So I work up from a starting load (from Quickload but comparing to other published data) and in crease either .5 grains or 1 grains increments until I get a clicker or stiff extraction. Then I back off 1-2 grains depending on case capacity and work around there.

Many times I exceed book velocities but pockets remain tight and extraction remains easy. Those are my metrics.

I’m not suggesting anyone else do the same but that is what has worked for me for 40 years.


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[Koda_]

I don’t know why this seems like a hard thing to pin down, but I can’t quite figure out how much pressure is too much. And most importantly - why.

The problem with handloading is there is no practical way for the average handloader to accurately measure chamber pressure. For that you need expensive test barrels that typically only the manufacturers can afford. The only way to know if you have too much pressure is to look for all the usual signs most handloaders discuss (bolt lift, etc.) then back off at least half a grain charge weight. Many handloaders run a pressure ladder as their first step in new load developments, just know where their safe window of operation is before they move on to ignition testing and then fine tuning an accurate handload.

I’ve fired decent amount of rounds that have ejector marks, and I hear guys talk about velocities that are too high and then they say they’re running hot, but they don’t seem to be worried about it.

This is a separate subject, there will always be people who are more comfortable pushing limits. It can be good, or bad. If your not comfortable pushing the limits then ignore the advice of those that do. Personally, while I want the most velocity I can get but group size and pressure signs dictate what I end up with, I dont push the max.

 

[JF_Idaho]

There is a recent Ultimate Reloader episode where they take pressure to the extreme.

 

[2y2c]

I really appreciate everyone’s experience and help here. I found it very interesting in that ultimate reloader video that they went way way way over pressure and only saw a little cratering. Eventually an ejector mark, and they were way over.


I didn’t quite understand what would have happened if they had kept going. It sounded like a primer would blow. Which would either mess with the trigger or shoot back around the firing pin? I’m not sure if I know exactly what would happen there. And then if it went beyond that, we’d have case head separation and have a stuck case in the chamber? Let’s say they had five times fired brass or lower quality brass. Would the pressure have been elsewhere rather than just cratering?

It seems that good brass and a well built action can take more than saami recommends, but when you cook a round in the chamber or have moisture, it looks like pressure could jump quickly.

 

[Koda_]

I found it very interesting in that ultimate reloader video that they went way way way over pressure and only saw a little cratering. Eventually an ejector mark, and they were way over.

I wouldn't take anything away from that video other than just entertainment.

One thing to consider intentionally running at max pressure is the temperature difference between summer and winter.

 

[Mike D Texas]

I really appreciate everyone’s experience and help here. I found it very interesting in that ultimate reloader video that they went way way way over pressure and only saw a little cratering. Eventually an ejector mark, and they were way over.


I didn’t quite understand what would have happened if they had kept going. It sounded like a primer would blow. Which would either mess with the trigger or shoot back around the firing pin? I’m not sure if I know exactly what would happen there. And then if it went beyond that, we’d have case head separation and have a stuck case in the chamber? Let’s say they had five times fired brass or lower quality brass. Would the pressure have been elsewhere rather than just cratering?

It seems that good brass and a well built action can take more than saami recommends, but when you cook a round in the chamber or have moisture, it looks like pressure could jump quickly.

The parts for that rifle were intentionally picked to maximize the amount of pressure that it could stand.


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[A382DWDZQ]

I didn’t quite understand what would have happened if they had kept going.

What he says it in the video was pretty clear. Your brass ruptures, your action blows up, and you go to the hospital.

 

[General RE LEE]

If you love your car, you wouldn’t red line it everytime you drove it.

 

[seand]

The problem with handloading is there is no practical way for the average handloader to accurately measure chamber pressure. For that you need expensive test barrels that typically only the manufacturers can afford. The only way to know if you have too much pressure is to look for all the usual signs most handloaders discuss (bolt lift, etc.) then back off at least half a grain charge weight. Many handloaders run a pressure ladder as their first step in new load developments, just know where their safe window of operation is before they move on to ignition testing and then fine tuning an accurate handload.

The most practical way to get an approximation of chamber pressure is still to look at the chronograph. Max book velocity is going to correlate better to max chamber pressure than CHE, reading primers, etc.

 

[Koda_]

The most practical way to get an approximation of chamber pressure is still to look at the chronograph. Max book velocity is going to correlate better to max chamber pressure than CHE, reading primers, etc.

If you have published load data, yes max velocity is one of the things to look for. So is upper velocity plateaus, those to me really stand out.

 

[JeffRaines]

For me...

Pressure = Velocity. Velocity = Pressure. Theres no other way to get a bullet going than to put pressure behind it. Its why I believe a good chronograph is a requirement to safely reload. You can tell at a glance what your pressure is. If the books are saying 2950 is max pressure and you're running 3050+, you're over pressure regardless of what signs may or may not be present on your brass/primer.

The only times this might be off is when you take an older cartridge into consideration like the 270, 308 or 30-06. From my understanding some of those book max pressures take into account older, weaker actions. You bring a modern action, with tight tolerances into the picture and you might be able to wring a bit more out, but even then I wouldn't go crazy.

Theres also a balance - if I'm shooting a 300 magnum of some sort, I want magnum velocities. It's pointless to have a big case and settle for 308 speeds. If I'm okay with 308 speeds, I'll just buy a 308.

As far as what happens and when, that's not something that anyone can answer because it all depends on your action, your brass, your barrel. If you've been running hot loads for forever, its more likely your action will fail more catastrophically and sooner because it's been run hard vs the action that's been kept within specs and you put one or two hot loads through it.

 

[Pharmseller]

Velocity
Velocity
Extractor marks
Bolt lift
Velocity

In that order.

Excess pressure is bad. High blood pressure increases the risk of stroke. You don’t want your rifle to stroke out, either.

My Tikka Varmint .223 had a TIA last year. Complete recovery but a neurosurgeon gave her a new firing pin.






P

 

[General RE LEE]

I loaded 50 rounds of 6 ARC at Hornady book maximum but my velocity was almost 100 FPS faster than book. Load was very accurate but ejector marks and stiff bolt lift on each shot. I fired 3 shots back to back and bolt was very stiff. I pulled bullets and dropped down a grain.

 

[Mikey_B79]

The important thing is to use reputable data from known good sources and corroborate that data with a chronograph.

If you are at maximum charge weight and are close to the posted velocity, I would call it good. If you are below maximum charge weight but at posted velocity, I would also call it good.

When you throw the loading manual out the window (so to speak) and change COAL to suit the chamber, use neck-sized brass, long drop tubes, different primers, etc then you will need to be diligent in observing necks, primers, case heads, and primer pockets on each piece of brass as you reach the max published charge weight with the intention of moving beyond the published max.

Each rifle will object to your reloading technique in its own way. It might sound a bit ridiculous but you really need to pay attention to what it is telling you when you start getting creative. Otherwise you'll end up with Bubba's pissin' hot handloads where a little brass ejecta to the face is okay and you save time by having the cases deprime themselves on firing.

 

[willfrye027]

Other than safety concerns, running in the red you are more likely to have equipment fail in the field.

I have a (very) hot 30-06 load that functions perfectly smooth even in the 100degree heat. But I know it’s a hot load.

I got my action super wet and had a little bit of water in the barrel to hunting some wet snow. I test fired just to see what would happen and pretty much locked up the bolt.

If there was an elk or mule deer instead of a rock and it needed a follow up shot I’d have been hosed!

 

[2y2c]

Other than safety concerns, running in the red you are more likely to have equipment fail in the field.

I have a (very) hot 30-06 load that functions perfectly smooth even in the 100degree heat. But I know it’s a hot load.

I got my action super wet and had a little bit of water in the barrel to hunting some wet snow. I test fired just to see what would happen and pretty much locked up the bolt.

If there was an elk or mule deer instead of a rock and it needed a follow up shot I’d have been hosed!

Does your hot load show any signs of pressure, or did it go from no signs straight to a locked up bolt? Was it just as likely to screw up the trigger or roast the firing pin or get a case stuck? What action are you using?

 

[2y2c]

I guess a few people have touched on why I haven’t found a solid answer to this question before. It sounds like it will vary depending on rifle and brass and circumstances for causing that failure.

For instance, I’m using a defiance action and once or twice fired lake city brass. It seems like I could be a decent amount over pressure (judged by velocity) without showing much more than flatter primers. I’m not saying I’m going to do that. I’m just speculating. If the velocity was higher than book for my barrel length, but I’ve never had ejector marks or a hard bolt lift, is it likely to be ok if there was moisture? Or is that too deep into the weeds or the unknown when it comes to how the brass was prepped, bolt nose clearance, etc?

 

[LaFever]

if you don't want to worry about it , stay under the reloading book maximum , the hottest loads are not always the most accurate . if you find a load that shoots well that is under the book maximum then that load will surely be lethal for whatever game you are pursuing
every rifle has a different hot load or maximum loads though the rifles won't be too different due to differences in manufacturing.
there are some people that run their handloads pretty hot and the published loads have " probably " taken this into consideration .
you're not missing or losing anything by following the instructions

 

[A382DWDZQ]

I guess a few people have touched on why I haven’t found a solid answer to this question before. It sounds like it will vary depending on rifle and brass and circumstances for causing that failure.

Exactly, you will not find a solid answer for something so ambiguous, and which includes “and circumstances”. This is something that the industry has spent a lot of resources researching and the technological advances that we enjoy today are the product of that.

is it likely to be ok if there was moisture?

How would you answer this, or propose for someone else to answer it? How much pressure do you think you’re at? How much do you think the brass in your chamber is capable of? How strong do you think your bolt lugs are? Are you talking about a chamber completely full of water, 15gr, 100gr, 3gr? You’ll have to quantify it to answer it. Then you determine what scenario is realistic for your risk tolerance.

 

[Savagehunter]

Your question being what happens. The answer it depends. Maybe a blown primer maybe case head separation maybe catastrophic failure and the fractured pieces of your rifle enter your skull and kill you. Metal fatigue and possible weakened metal over as many as 5000 rounds or as few as 1. Manufacturing flaws can and do exist in any product that we make realistically an action could fail at aven sami spec. So why do people go over same reason people jump out of airplanes. Living on the edge is a human condition. Myself I would never jump out of a perfectly good airplane.