Pressure: when is too much and why?

[willfrye027]

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?

This is lapua 30-06 brass with essentially a bore rider bullet no real load data out there. In a tikka action, older t3 that is smoother and must have tighter tolerance than any of my newer ones.

It’s a half grain below ejector marks…but a piece of lapua brass only lasts 4-5 firings. That was really my biggest clue that I’m way up there in pressure.

Blew the primer out and had to basically hammer the bolt open. Some gas cutting on the bolt face..but also not the first time I’ve blown a primer. It seems to hide pressure well for whatever reason. Has not seemed to affect accuracy or subsequent function.

When I’ve settled on a load I do like to reload one or two pieces over and over to make sure I’m getting the longevity I need. I hardly ever shoot that 30-06 except at game animals so it didn’t bother me too much…but next time I load more of that I’ll drop a grain at least.

 

[Shortschaf]

I’ve been reloading for less than two years. I spent a lot of time reading on a bunch of different forums, and watched a lot of videos. 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.

"Too much pressure" is "what pressure can you stomach"
On this topic, in terms of importance: 1st is your safety, 2nd is brass life.
In terms of likelihood: brass damage shows itself well before gun explosions

And most importantly - why. It seems like the first thing we’d all want to know. I know signs, and I know I’ve been over pressure, but I’d like to know what happens in what order, and what the danger is.

Brass life shortening, pierced primers and gas in your face, then action explosions. In that order. Sprinkle in case-head-seperation anywhere, since thats a headspace/reloading/bolt clearance issue most often.

Yes, I know death and dismemberment are the dangers, but I’d like to know specifically how and why.

Here is an example of what dangerous pressure can and will do to you. Though this was not a reloading issue, this still serves as the epitome of "reloading done wrong"

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. Even Jake from unknown says he’ll load stuff super hot because he doesn’t care how many firings he gets out of the brass, and he knows the action can take it. On the other hand, some guys are extremely wary of getting velocities over book max.

Only you can choose where you draw the line. Personally, if I don't have heavy bolt lift, I'm far inside the safety zone of the action's strength. I don't really care about ejector swipes.

I don’t mind if I only get a few firings out of brass, but I want to know what the real danger is in order of likelihood as pressure increases. I know of case head separation, but I don’t really know what else would happen before that. And I’d really like to know what the dangers are.

See above.
different brass headstamps/lots behaves differently to otherwise same loads/pressure. That's one of the complications in understanding this topic

 

[wind gypsy]

To me too hot is if you’re worried about blowing primers and locking up your bolt in wet conditions. On a clean bore, dry, and 40 degrees everything can run like a top. Get a lot of fouling, some moisture and it can be too hot multiple grains lower.

 

[Pickettpuncher]

 

[TaperPin]

Velocity does not translate as closely to pressure to use it to judge max loads. Some bores are tighter than others - I have had a rifle that maxes out almost 100 fps lower than published max, but some would just go ahead and load it up until the published velocity is reached? Which published velocity do you use for this? In half a dozen different manuals, velocities vary all over the place - just load it up to equal the fastest book load? Nah.

 

[JGRaider]

Velocity does not translate as closely to pressure to use it to judge max loads. Some bores are tighter than others - I have had a rifle that maxes out almost 100 fps lower than published max, but some would just go ahead and load it up until the published velocity is reached? Which published velocity do you use for this? In half a dozen different manuals, velocities vary all over the place - just load it up to equal the fastest book load? Nah.

I have to disagree. Without equipment to measure pressures (strain gauge), velocity is absolutely the best indication of pressure. Can't have high velocities without high pressure.

 

[wind gypsy]

Velocity does not translate as closely to pressure to use it to judge max loads. Some bores are tighter than others - I have had a rifle that maxes out almost 100 fps lower than published max, but some would just go ahead and load it up until the published velocity is reached? Which published velocity do you use for this? In half a dozen different manuals, velocities vary all over the place - just load it up to equal the fastest book load? Nah.

The velocity comes into play when it's obvious you're going faster than common sense and good data suggests it ought to be but still not seeing pressure signs.

A personal example - 6.5x47 lapua cases hide pressure very well. I have had 140 class bullets exceed 2800 FPS easily with H4350 and no notable pressure signs. A little understanding and sense says a case that is near identical to a creedmoor case but a little smaller isn't exceeding creedmoor max book velocities with the same powder unless there's a lot of pressure helping it do so. Therefor i'm not going to wait until I have a fouled bore, hot weather, or get water in my gun and start piercing primers. I'm going to back it down a little because the velocity is telling a story.

If you're getting pressure signs but not getting book velocity, well then you dont need velocity to tell you to back off.. I.E - the velocity isn't to tell you when you're at safe pressures, it's to tell you when you don't know you're at high pressures.

 

[TaperPin]

I have to disagree. Without equipment to measure pressures (strain gauge), velocity is absolutely the best indication of pressure. Can't have high velocities without high pressure.

Some barrels/chambers/brass shoot slightly slow and some shoot fast.

I’ve had a couple of rifles that would have very short case life if loaded to published max velocity. Based on that alone, I’m 100% convinced velocity is too variable.

Likewise, I’ve had a rifle that shot 100 fps over max without as much as an ejector mark and case life was over a dozen reloads. Based on that rifle alone I’m 100% convinced velocity is too variable.

 

[TaperPin]

That doesn’t mean I don’t look at velocity - it’s a good secondary indicator that a load is close to a max, just not the ultimate determination of max.

 

[HighUintas]

That UR video demonstrates how you can be in the scary pressure territory without knowing it if you're only using brass and primer inspection for judging pressure.

Shooting some 6.5cm loads at 1gr over Hornady book max, I had zero pressure signs on the brass but the primer was extruding into the firing pin hole ... Similar situation to the video. My velocity was 100fps over book max also so I know I was high on pressure but it was a little confusing to see primer extrusion without brass pressure signs. That load will definitely be backed down at least a grain.

 

[Wrench]

This is lapua 30-06 brass with essentially a bore rider bullet no real load data out there. In a tikka action, older t3 that is smoother and must have tighter tolerance than any of my newer ones.

It’s a half grain below ejector marks…but a piece of lapua brass only lasts 4-5 firings. That was really my biggest clue that I’m way up there in pressure.

Blew the primer out and had to basically hammer the bolt open. Some gas cutting on the bolt face..but also not the first time I’ve blown a primer. It seems to hide pressure well for whatever reason. Has not seemed to affect accuracy or subsequent function.

When I’ve settled on a load I do like to reload one or two pieces over and over to make sure I’m getting the longevity I need. I hardly ever shoot that 30-06 except at game animals so it didn’t bother me too much…but next time I load more of that I’ll drop a grain at least.

.5grs in a 30-06 sized cartridge is around 1/2 of 1%. That close is lost in the noise. Not that we don't all do it occasionally, but it's hardly statically safer.

 

[TaperPin]

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

I like that they measured case heads - halfway through at 44 gr the head expansion of .0006” would have been over pressure at least a few grains to me. It would have been nice if they showed expansion at every increment. There was only the hand written fired case head measurements without a starting number - every case will measure slightly differently, so without a starting number it doesn’t mean much, and the measurement has to be taken at the exact same spot because diameter varies all around the head. I was also disappointed they didnt reload a few cases multiple times to show how the thinning of the web of the case head progresses and case head diameter increases up until a partial separation is eminent.

The Bat action is super strong and the firing pin hole is a tight fit with the firing pin, so a factory rifle might have shown issues much sooner. I wouldn’t want to try that with a relatively soft Remington action.

Still, a nice demonstration.

 

[Castle Rock]

View attachment 697888

Ah, the famous Model 70 pre 64 that people are waxing on about here recently , and the elephant in the room

 

[willfrye027]

.5grs in a 30-06 sized cartridge is around 1/2 of 1%. That close is lost in the noise. Not that we don't all do it occasionally, but it's hardly statically safer.

Yep I hear you there. This particular load functions well but with a moist chamber it’s definitely over the top. I don’t know how much additional PSI a wet chamber adds…I’ve had factory ammo extract super stiff when wet.

It’s a gun that I rarely use but when I finish killing pigs and blacktails with the rounds I have left, the load is getting reduced by 75-100fps regardless of the pressure signs. I’m too lazy to pull the remaining 30 or so..I’ll just make sure the gun stays dry for now.

It was more of an example of a system that seems to be “hiding” pressure very well, until it doesn’t. And what I would consider the pitfall of being too close to the edge. My daily drivers the brass will last at least 8-10 firings and may have stiff extraction when moist but certainly won’t blow a primer or lock up the bolt.

 

[SouthPaw]

The real problem happens when you touch one off in the rain, or snow and have some moisture on the round/chamber.

I load low because of that. If I want more speed I’ll move to a bigger case.

This is where I've landed for the most part.

I don’t know how much additional PSI a wet chamber adds…I’ve had factory ammo extract super stiff when wet.

I'd love to know this too, but I'm sure its variable based on lots of factors.

I went on a recent hunt using a load that was half grain under book max with a longer than book OAL, zero pressure signs in normal conditions and velocity below book max. It rained nonstop for five days straight and was raining during the stalk, the fired shot that killed the elk came with a shiny ejector mark, bright swipe and heavy bolt lift.

 

[Steve300xcw]

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

That is a horrible example.

And yes I do

 

[Steve300xcw]

I have a ruger .223 that will pierce a primer fairly quick. Step up to a Rem 7-1/2 and I can go quite a bit more.


I had some pretty hot loads of RL22 that sat in a truck, in the sun all day. The entire primer was removed when I shot one of those rounds off that afternoon. Cut up the bolt face enough to block off the ejector hole. Kinda changed my outlook on hot rodding ammo

 

[willfrye027]

This is where I've landed for the most part.


I'd love to know this too, but I'm sure its variable based on lots of factors.

I went on a recent hunt using a load that was half grain under book max with a longer than book OAL, zero pressure signs in normal conditions and velocity below book max. It rained nonstop for five days straight and was raining during the stalk, the fired shot that killed the elk came with a shiny ejector mark, bright swipe and heavy bolt lift.

I’ve had that with factory ammo too..so idk what the right answer is

 

[wind gypsy]

Yep I hear you there. This particular load functions well but with a moist chamber it’s definitely over the top. I don’t know how much additional PSI a wet chamber adds…I’ve had factory ammo extract super stiff when wet.

My understanding is that it might not be so much about increasing pressure but the moisture preventing the brass from gripping the chamber wall like it's supposed to so you get a lot more bolt thrust.

 

[Castle Rock]

Bolt thrust due to the case not gripping the chamber walls is certainly a factor
The other issue is most reloading dies make the case a lot smaller than they have to (similarly a lot of factory ammunition is considerably smaller too)

Because water is filling the void between the case and chamber and water is basically non compressible this results in a smaller effective chamber and reduced volume equals increased pressure