Pressure: when is too much and why?

[Castle Rock]

Millions of rounds of saturated ammo have been fired in water soaked guns in conflicts around the world without issue
The lesson is don’t load on the ragged edge and you will be fine

 

[Shortschaf]

My gunsmiths theory on why the first shot is regularly slower on the chrono has to do with the barrel temperature. I’d be interested in more tests

I'd be willing to bet that the first "slow" shot would fall within the ES of a large sample size. Shooters are obsessed with theorizing about the dynamics of ballistics and why something did what, the problem is they don't understand statistics and put merit into small data sets. If you repeat a cold bore shot 30x and it falls outside the ES of a subsequent 30 shot string, you probably have something there. But Running 5 shots over the chrono and thinking the cold bore is an outlier because it was 20fps slower than the next 4 is just playing within some serious noise.

Without knowing the background of the conversation with said gunsmith, or when people are seeing "slow cold bores", I offer one side note:

The first shot from a freshly cleaned barrel is often consistently below (up to 100fps) a gun's average velocity. That is normal. Ignore if at the range, but maybe be aware of it if that shot is meant for an animal a long ways away

 

[TX_Diver]

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.

Do you test this during load development at all? Throw a wet round in the chamber or anything?

 

[35WhelenAI]

Wipe the ammo dry before chambering, tape the barrel and leave all the speculation behind as it becomes a non issue.

Would not deliberately try it, water is not compressible and it's not a world conflict in the field, lives are not on the line. Keep things dry and don't load so hot as to need to wonder about it.

 

[35WhelenAI]

As an aside, my brother brought a friend from another state with him on our 2nd season elk hunt in Colorado last year. Guy had a 6.5 Creedmoor and hunted a full day in the field in falling snow with an open muzzle. Had been told to tape the muzzle. Next morning, he came out of the tent (5 deg F) and couldn't open the bolt. Idiot had left a round chambered overnight and it froze the bullet into the throat.

Got it opened, but only the case came out and dumped powder all thru the action. Had to warm it by the fire and even then, used a cleaning rod down the bore to force the bullet out. If he hadn't tried to open his bolt in the morning, and he had fired that round, I guarantee he'd have had a big problem in the woods.

Tape your barrel, should be common knowledge.

 

[A382DWDZQ]

I’m not trying to blow myself up. I do want to reload safely and that means trying to understand how to assess how my loads are behaving without a laboratory setup.

This is done using a chronograph and reading the pressure signs. Between those two things, you should know when you’re getting into dangerous territory. Aside from that, fork out a little extra $ on QuickLoad or grab a copy of Gordon’s Reloading Tool. Quickload and GRT are particularly useful for determining what the impact of seating depth will be, but your chronograph will tell you that too.

 

[35WhelenAI]

Aside from exceptions, rather than rules, velocity equals pressure. Seems some (many) abosolutely "know" (through their experience, not established sensibility) their rifles are the exceptions much more the rule. Not being harsh, but yes, being harsh. It's ridiculous to chase that last "nth" degree of velocity in the small cased fan boy cartridges to flatten trajectory a smidgen to compare numbers on a forum. It's the day and age we live in, believe in ones's individual experience/ignorance vs 100+ years of others experience.

 

[mt terry d]

Seems It's ridiculous to chase that last "nth" degree of velocity in the small cased fan boy cartridges to flatten trajectory a smidgen to compare numbers on a forum. It's the day and age we live in, believe in ones's individual experience/ignorance vs 100+ years of others experience.

I haven’t read anything in this thread implying anyone wants to “chase the nth degree of velocity. Maybe I missed it. I’m pretty good at missing.

 

[Lawnboi]

Do you test this during load development at all? Throw a wet round in the chamber or anything?

I do after the barrel is done speeding up. So after 200 or so rounds when I have my load. I load fairly low, if I find pressure I back off a grain plus.

I’ll sun soak a few and shoot on a rainy day and leave one to get wet. Usually wrecks the brass but I want to know I’m not going to be stuck with a locked up gun or popped primer in a match/in the field.

I don’t necessarily condone people just going out and getting rounds wet and shooting without some serious thought put into it.

It’s something alot of guys who are loading on the heels of pressure don’t think about. See it all the time at matches when it rains. People ending up with rifles that will no longer operate, or a few blow primers leading to consistent failure.

 

[wind gypsy]

It's ridiculous to chase that last "nth" degree of velocity in the small cased fan boy cartridges to flatten trajectory a smidgen to compare numbers on a forum.

Because nobody chases the nth degree of velocity with bigger magnums or 308s or the "back to back world war champ!"..

 

[centershot]

IF I want more speed/power than published book max. I use a bigger gun.

 

[Harvey_NW]

Because nobody chases the nth degree of velocity with bigger magnums or 308s or the "back to back world war champ!"..

"Jimmy call the Dr, papaw's strokin out over a question about pressure on the interwebs!"

 

[Shontwelve]

Gas guns will also show slight differences in initial pressure signs that bolt guns.

 

[Tell]

Reading pressure from a primer might not give the full story. I had cci400’s flattening pretty well with a little cratering, and then swapped to rem 7 1/2’s and the edges are perfectly rounded still and no sign of any pressure. I know the 400s have a thinner cup and the 7 1/2’s have a thicker one. Using the 400s, I’d say there’s pressure. Using the Remingtons, there are no signs at all.

I have had the rounds out in the sun getting hot, and they’ve been in the chamber for a bit while it’s hot after a good string of fire and there have never been any ejector marks, click, stiff bolt or primer marks (with Remington). The chamber is throated pretty deep, and rounds are loaded long but nowhere near jam.

So even though cci reads hot, it seems to me that it’s a safe load since I’ve shot a couple hundred of them in varying conditions with no brass or bolt problems.

 

[Marbles]

It really depends on how you think. I like a safety margin, so I don't play with high pressure much.

I'll put it in ringing/climbing terms and safety factor.

Safety factor accounts for how much error you can have in your load weight before breaking the system. You will not test every system to failure, and most components will not be new, so the calculated strength is best case.

Life safety should have a safety factor of 10. So if you need to static load a 200 pound man the average break strength of every component must be 2000 pounds or above. Thus, lots must go wrong for something to break and the person die.

Can a rope with a 250 pound mean breaking strength work? Yes. Can 550 cord work? Yes. Unless the cost of not doing it is catastrophic and you have nothing else available, one is flat stupid to use such systems.

Now, safe pressure is like a safety factor of 10, it is the standard and makes catastrophic failure very unlikely. As you push that up, you have less and less room for error. Now, you are running 74K PSI load, the chamber is wet increasing bolt thrust, you have a carbon ring, the bore has a slight amount of dirt in it from being in the field, and this load is on the hot side of the distribution. No one of those would result in failure, but all might come together and at best leave you with no follow up shot. At worst, well you get the point.

100 fps is not worth it to me. The brass and action don't matter. Everyone else is free to do as they please.