Primer Signs & Pressure

[35WhelenAI]

Do it with the same lot of cases and establish a baseline each time you change case brands and it's not a crapshoot.

 

[35WhelenAI]

I wanted to develop a load for the Barnes 200 TTSX for my 35 Whelen AI using Power Pro varmint powder. Spear shows fantastic velocity with that powder and 180 and 220 grain bullets. I extrapolated the load data, established a safe starting load and used case head expansion to find the max for that load. Based on years and years of experience with case head expansion measurents with other safe loads using traditional powders, the load I worked up fit right in line.

Different primers different cases different powder lots, what one guy thinks is light bolt resistance may not be what another guy thinks. Case head measurement is about the only definitive way to put a number behind it.

 

[AkMtnRunner]

Negative. A dial micrometer to 4 decimal places. .0004-.0006. Your measurements are quite a magnitude greater than what you should be measuring. 45/1000-55/1000 is what you are calling your measurement, I'm talking for 4/10000-6/10000. If you are measuring that much head expansion it's either a blade micrometer which is not capable of the accuracy or way overboard. You must use a dial micrometer. Different than what you typically use for reloading.

Yep, I just have a standard micrometer that measures to the nearest .5 thousandths. I measured 4.5/1000 to 5.5/1000. Still one order of magnitude different than yours.

 

[35WhelenAI]

Copy that. Dial micrometer.

 

[BBob]

standard micrometer

Micrometer or caliper?

Dial micrometer.

What are you actually referring to as a dial micrometer?

 

[BBob]

This is the proper tool for measuring case webs for expansion. A tenths reading blade mic:

The reason it’s the proper tool is if you attempt to use a std mic the base of the case can potentially and likely interfere with your measurement. There are a few exceptions:

A digital caliper with a resolution of .0005” isn’t good enough for this:

 

[Bowfinn]

So is the spritz of water cooling the brass or filling space in the chamber?

From what I’ve heard/understand it’s filling space in the chamber with something that’s not easily compressed.

 

[35WhelenAI]

Micrometer or caliper?
View attachment 890426

What are you actually referring to as a dial micrometer?

Apologies on the unclear terminology. Micrometer or outside micrometer would have been better on my part. Ages ago I was introduced to it as a dial micrometer because the handle was dialed at the base to get the measurement.

 

[TaperPin]

Case head diameter measurement technique barely comes up in conversations even though it should, but many of the old reloading manuals recommended it and before small vintage bullet companies could afford pressure guns and barrels in every cartridge it was used to produce early reloading data.

A .0001” micrometer doesn’t have to be fancy to work well. Even this Shars model can give measurements that are quite usable. Other nicer brands are available used for not much more.

 

[35WhelenAI]

It is a very good tool but most folks don't bring it up in conversation because they don't know about it and/or it takes a bit of work to do.

 

[TaperPin]

It is a very good tool but most folks don't bring it up in conversation because they don't know about it and/or it takes a bit of work to do.

Wouldn’t you say it’s actually fun to see the case head measurements? I love to see in real time what the case is doing.

 

[35WhelenAI]

Absolutely, no better feeling than getting good velocity and accuracy out of the load and returning to the bench to find the case head has expanded within a safe range.

 

[parshal]

So is the spritz of water cooling the brass or filling space in the chamber?

Water isn’t compressible so it’s filling space.

Wet cases are easily a thing when hunting and it increases pressure more quickly than temperature. People are worried about temperature but never about water. You see sticky and stuck bolts at matches when it rains from loads right at the edge of pressure.

 

[AkMtnRunner]

Well, it looks like I owe you folks an apology for my miscommunication. I am in fact using a digital caliper. Thanks Bbob for pointing to that so obviously. The good news, this experience on this site will likely only cost be less than $100 this time.

I appreciate the help. Somehow, I've never come across this way of finding pressure.

 

[35WhelenAI]

The moral of this thread is don't chase velocity unless more than reasonably certain the pressure monitoring methods used indicate a load that's not over pressure.

 

[Ucsdryder]

I didn’t read every thread on here but someone told me a while back when I started reloading, pay attention to max velocity and don’t get so much in the weeds on powder. Velocity = pressure. If you’re beating max velocity with same barrel length, that velocity isn’t free, it comes with increased pressure

 

[AkMtnRunner]

The moral of this thread is don't chase velocity unless more than reasonably certain the pressure monitoring methods used indicate a load that's not over pressure.

Maybe I didn't make it clear, but I certainly am not chasing velocity. Rather, I am seeking to know where excessive pressure is, so that I know where a safe range of charges is to use for further load development.

It's still unknown whether I reached max pressure or not. The case expansions I measured, with an incorrect tool, of low charge weights were also an order of magnitude larger than values associated with max pressure, so those are likely nonsensical. Having a low charge weight and 400 fps less than expected max velocity is better information than a measurement with the wrong tool.

What I take from this thread is there are many possible data points to look to for pressure signs, and to use the right tool.

 

[grizz19]

What velocity were you getting @ book max? Barnes loading data tends to have max charges higher than other data I've found for the same bullet so be cautious.

I'm working on load development for my 7PRC same as you. However while I have H4831sc, I'm starting with H1000 using the 160LRX.

Currently in the same process as you. Hoping to get my first ladder test fired this weekend. I’d be interested to hear what you come up with

 

[35WhelenAI]

That comment wasn't directed at anybody in particular. Many people potentially could read this thread, and the few that say no need to worry, are giving bad advice and it's due diligence to state it plainly. Looking forward to hearing how things go as you continue working on the load.

 

[SDHNTR]

That comment wasn't directed at anybody in particular. Many people potentially could read this thread, and the few that say no need to worry, are giving bad advice and it's due diligence to state it plainly. Looking forward to hearing how things go as you continue working on the load.

Have you actually seen a situation where case head expansion reaches an unsafe level before a primer flattens, or craters, or stiff bolt or an ejector mark? I surely haven’t.