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#2978218 - 07/19/16 07:13 PM Understanding Pressure
orkan Offline
Die Hard Member II

Registered: 06/27/03
Posts: 1745
Loc: Western SD


Primal Rights, Inc - Understanding Pressure

Just finished up an article that should help people gain a better understanding of the pressure at play in their firearms.

Let me know if you have any questions and I look forward to your comments!

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#2978292 - 07/19/16 11:23 PM Re: Understanding Pressure [Re: orkan]
SlickerThanSnot Offline
PM senior

Registered: 01/31/14
Posts: 5019
Loc: stuck in a fence
thank you for doing that article. has great pictures and explanations. will come in handy for future reference.

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#2978313 - 07/20/16 12:35 AM Re: Understanding Pressure [Re: orkan]
Plant.One Online
Die Hard Member with a vengeance

Registered: 02/12/15
Posts: 4143
Loc: Oakland County, MI
thats a wondeful writeup - hopefully you get lots of google hits with that.


i remember reading on another forum where a fella said that blown primers were just fine, as long as there were only "a few here and there". IIRC he got offended when i asked him where he shot so that i'd avoid that range so i could never end up on the bench next to where he was shooting.
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All reloading info shared is based on my experiences in my guns. Follow safe reloading practice and work up loads from published minimum data.
This disclaimer will self destruct in 10 seconds.


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#2978325 - 07/20/16 02:38 AM Re: Understanding Pressure [Re: orkan]
reaper4 Offline
Die Hard Member II

Registered: 02/25/14
Posts: 1901
Loc: maryland eastern shore
Great write up and it really illustrated clearly signs I should be looking for as a relatively new reloader. I hear things and have a hard time determining exactly what that looks like on a case and now I know. I have stayed in the lower charge weights and still seen ejector print on cases and had to ask an older more experienced reloader what that meant. Thanks for the great info
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#2978329 - 07/20/16 06:43 AM Re: Understanding Pressure [Re: reaper4]
7887mm08 Online
Die Hard Member

Registered: 08/15/10
Posts: 505
Loc: upstate n.y.
Seeing is believing! Thank you

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#2978331 - 07/20/16 07:06 AM Re: Understanding Pressure [Re: orkan]
Lefty SRH Offline
Die Hard Member III

Registered: 01/09/14
Posts: 2024
Loc: North AL
Good article, thank you.
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#2978339 - 07/20/16 08:38 AM Re: Understanding Pressure [Re: orkan]
mbaysinger89 Online
Die Hard Member II

Registered: 07/08/13
Posts: 1179
Loc: kansas
Great article.

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#2978349 - 07/20/16 10:23 AM Re: Understanding Pressure [Re: orkan]
vanhornet Offline
Seasoned Member

Registered: 04/30/15
Posts: 296
Loc: mid mo
Excellent write-up. Thanks for posting.

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#2978438 - 07/20/16 04:25 PM Re: Understanding Pressure [Re: orkan]
dan158 Offline
Die Hard Member II

Registered: 03/31/14
Posts: 1308
Loc: PA
Lets say one shut off the gas system so bolt wont move for an AR.
One ejects cases manually by pulling the BCG back.. One has no swipe marks and brass looks fine.. But when gas system is running it leaves bad markings. Is it considered over pressure or just the timing at which can not be slowed down enough to function as a semi auto? There would be more time for the brass to cool down by manually eject with gas off than if being ripped out so fast before has a chance to cool and shrink.. Over pressure or not?? Then what would the signs be? The same as a bolt rifle then?? Thanks. Dan

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#2978444 - 07/20/16 04:53 PM Re: Understanding Pressure [Re: dan158]
orkan Offline
Die Hard Member II

Registered: 06/27/03
Posts: 1745
Loc: Western SD
Originally Posted By: dan158
Lets say one shut off the gas system so bolt wont move for an AR.
One ejects cases manually by pulling the BCG back.. One has no swipe marks and brass looks fine.. But when gas system is running it leaves bad markings. Is it considered over pressure or just the timing at which can not be slowed down enough to function as a semi auto? There would be more time for the brass to cool down by manually eject with gas off than if being ripped out so fast before has a chance to cool and shrink.. Over pressure or not?? Then what would the signs be? The same as a bolt rifle then?? Thanks. Dan
I'm sorry but I have not done adequate testing to confidently answer your question, and I specialize in work with bolt action precision rifles.

My speculation would be that the gas system is part of the "expansion chamber" in a semi-auto, as is necessary for proper function in a gas-driven system. In order to read pressure signs effectively, the entire system must be functioning as designed. It is no surprise that bolt action rifles are considered to be much easier to work with, as this variable does not exist. There is no cyclic "timing" to worry about with bolt rifles. While I'm certain that the pressure shown in your hypothetical should be viewed as "real," I have not done adequate testing to tell you why it appears in semi-auto mode and not when the bolt is remaining locked. Perhaps someone with more experience with semi-auto's can comment.

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#2978450 - 07/20/16 05:30 PM Re: Understanding Pressure [Re: orkan]
GLShooter Offline
PM Sponsor

Registered: 01/09/05
Posts: 4928
Loc: AZ
You would be looking at case head expansion and primers on the home front along with chronograph numbers on the manual; operated rifle just exactly like a bolt action rifle. The gas system is opening up when there is still pressure on the cartridge effectively turning it into a rocket hitting the bolt face ripping on rims and pounding the brass down into the ejector hole. The brass is hot and very elastic at that point. Hence the fact that you can fire ten rounds in the same AR chamber and get three or four different shoulder height readings. The earlier it opens, as in over gassed, the more violence to your case heads will be observed. The adjustable block or a heavier spring/bolt combination will mitigate some of these issues of observed over pressure indicators. Also be aware that a large firing pin tunnel in concert with a small firing pin will give false signs of pressure as this will induce cratering. Modern Remington BA rifles show this all the time with KNOWN lower pressure loadings.

Greg
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#2978458 - 07/20/16 06:30 PM Re: Understanding Pressure [Re: orkan]
cherokeetracker Offline
Seasoned Member

Registered: 01/05/15
Posts: 395
Loc: Texas
Orkan Good Article, WTG.

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#2978499 - 07/20/16 08:53 PM Re: Understanding Pressure [Re: orkan]
Rusty Black Offline
Die Hard Member

Registered: 03/06/13
Posts: 752
Loc: Southeast,Pa
Great article....thankyou

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#2979120 - 07/23/16 09:11 AM Re: Understanding Pressure [Re: orkan]
Kermit in Va. Offline
Predator Master

Registered: 01/22/16
Posts: 64
Loc: Va. USA
Thanks...
Every reloader should see this.


Kermit

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#2979125 - 07/23/16 10:20 AM Re: Understanding Pressure [Re: orkan]
ackleyman Online
PM senior

Registered: 01/08/03
Posts: 8407
Loc: Hickville
Best article that I have ever read on pressure! Thanks for putting so much time and effort into this article!

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#2979144 - 07/23/16 12:03 PM Re: Understanding Pressure [Re: orkan]
204 AR Offline
Die Hard Member with a vengeance

Registered: 01/31/10
Posts: 4586
Loc: Nebraska
Ditto what ackleyman said!
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#2979492 - 07/24/16 09:29 PM Re: Understanding Pressure [Re: orkan]
Bowhunt Offline
Die Hard Member

Registered: 11/28/15
Posts: 753
Loc: Illinois
Fantastic article! Great job and thanks so much for posting.
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#2984130 - 08/10/16 03:44 PM Re: Understanding Pressure [Re: orkan]
jpx2rk Offline
Seasoned Member

Registered: 01/24/16
Posts: 162
Loc: Tennessee
Good read. At what level of magnification were the pictures taken? Can you see most or all of the danger signs with a 4x magnifying glass, or is stronger magnification needed??

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#2984810 - 08/12/16 08:25 PM Re: Understanding Pressure [Re: orkan]
orkan Offline
Die Hard Member II

Registered: 06/27/03
Posts: 1745
Loc: Western SD
The pics were taken with a special "macro" lens on my DSLR. Here is the lens: http://amzn.to/29KFZH8

You can usually see pressure signs with the naked eye. The images were high resolution so that the effects could be easily seen by anyone reading. Any magnification will help however. The illuminated loupe I mention in the article will work quite well. Here it is: http://amzn.to/29KGAs4

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#2989389 - 08/29/16 05:16 PM Re: Understanding Pressure [Re: orkan]
Mark204 Offline
Seasoned Member

Registered: 03/12/16
Posts: 352
Loc: Midwest
Wow...written in a way that "average folks" can understand. The pics were essential in getting a grasp on what you were trying to convey. Thank you!!

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#2998219 - 10/07/16 09:48 AM Re: Understanding Pressure [Re: orkan]
Jason B Offline
Predator Master

Registered: 08/01/16
Posts: 78
Loc: Corn Country, Central IN
Great Article.

I will echo what Mark204 said in that it was written for the "average folk". The pictures made it very easy to follow and understand.

Thanks orkan!!

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#2998595 - 10/08/16 09:24 PM Re: Understanding Pressure [Re: orkan]
why Online
Die Hard Member

Registered: 08/29/14
Posts: 666
Loc: md eastern shore
I didn't read this untill today. Very informative, I learned a few things. Thank you.

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#2999488 - 10/12/16 01:26 PM Re: Understanding Pressure [Re: orkan]
SteWil234 Offline
New Member

Registered: 10/02/14
Posts: 13
Loc: Utah
Thank You, some very helpful information.

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#3001504 - 10/21/16 08:57 PM Re: Understanding Pressure [Re: orkan]
whispig Offline
Predator Master

Registered: 01/10/11
Posts: 64
Loc: virginia
Great read. Just goes to show how much I don't know... VERY much appreciated.

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#3006493 - 11/08/16 09:59 PM Re: Understanding Pressure [Re: orkan]
Nitroman Offline
Seasoned Member

Registered: 01/28/12
Posts: 277
Loc: Southwest Alaska
Temperature increases the RATE of a chemical reaction, which is why loads that work on a 40* day will extrude brass on a 110* day in the sun, not the AMOUNT of energy.

Looking at that Mauser bolt that had the lugs sheared off; unfortunately people aren't very smart these days, lots of stupid going around, and they do not read the loading manuals and load to velocity, they load to what is in the book and wonder why things go wrong.

The only way to truly know what is going on inside your rifle is to use pressure testing equipment such as Pressure Trace and a good chronograph like the Oehler 35p.

Good article.
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#3006682 - 11/09/16 09:01 AM Re: Understanding Pressure [Re: orkan]
NV Bill Offline
Seasoned Member

Registered: 11/06/13
Posts: 182
Loc: Columbus, MT
Well done article, thank you for taking the time to put all that info together with photos.

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#3008362 - 11/14/16 10:14 PM Re: Understanding Pressure [Re: NV Bill]
Wyodogger Offline
Junior Member

Registered: 09/21/16
Posts: 37
Loc: WY
Very helpful article!

BTW the blown-up rifle belonged to Chris Comer (RIP), a shooting buddy, a vet whose father died in WWII on Peleliu, and one of the nicest men you'd ever want to know.

Fulton armory said the barrel was made of a bad batch of steel that was held at too high a temp too long. Consequently, the steel molecules were too big, which eventually caused the blow-up. It was not a high pressure load. That was also shown by looking at the primer of the round in the chamber when it blew up; no pressure signs.

To add insult to Chris's injury, he couldn't replace the rifle as it was grandfathered under one of Kalifornia's goofy AW laws. I'm so glad I left that socialist, leftist hellhole.

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#3010335 - 11/21/16 08:02 PM Re: Understanding Pressure [Re: orkan]
sakalmon Offline
New Member

Registered: 11/03/16
Posts: 21
Loc: colorado
Awesome! I will reread several times until it all sinks in.

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#3026236 - 01/01/17 02:11 PM Re: Understanding Pressure [Re: sakalmon]
prairiefire Offline
Die Hard Member

Registered: 08/27/12
Posts: 714
Loc: Nebraska
For a relative reloading newly (only been at it for three years) this was an eye opening article. Made me take a step back and realize how complex accurate reloading can be and how one must never become complacent. Thanks!!

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#3033614 - 01/17/17 05:12 AM Re: Understanding Pressure [Re: orkan]
Strudy68 Offline
Junior Member

Registered: 01/09/17
Posts: 45
Loc: SE Iowa
Very good read!!! nice to see to step by step surprised that more pressure didn't have the effect that one would think....

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#3034810 - 01/19/17 04:33 PM Re: Understanding Pressure [Re: orkan]
GhostsoftheGrass Offline
Seasoned Member

Registered: 01/09/13
Posts: 191
Loc: NE
Very good! Thank you, sir!

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#3140369 - 03/20/18 06:07 AM Re: Understanding Pressure [Re: GhostsoftheGrass]
Bauxite Offline
New Member

Registered: 06/17/17
Posts: 4
Loc: The Jungles of Arkansas
Let me say thank you, too. Excellent.
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#3157218 - 08/02/18 12:03 AM Re: Understanding Pressure [Re: orkan]
Wa_Coyote_Hunter Offline
Die Hard Member

Registered: 12/16/06
Posts: 745
Loc: central washington
nice read saved on my computer for future reading. got a 357 mag from my uncle 30 years ago. with some reloads. fired a few rounds then bang pierced a primer. the sound of the shot sounded like it doubled. disposed of the rest of those rounds in a hurry.
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#3174042 - 11/27/18 11:08 PM Re: Understanding Pressure [Re: orkan]
Predzys Offline
New Member

Registered: 11/19/18
Posts: 7
Loc: IL
Nice write up

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#3187905 - 01/23/19 09:14 PM Re: Understanding Pressure [Re: orkan]
Flesh Eater Offline
Die Hard Member

Registered: 03/09/17
Posts: 665
Loc: 2D Pennsylvania
Very good article!

I’m thinking about getting into reloading and this was an eye opener even about factory ammo! Which after reading it I checked some casings on my once fired .17 Hornet brass. Sure enough, the Hornady 25 grain JHP was hot enough to make the primer look like your early pictures of cratering.

My question about the oil is how do you deal with rifles that get ice all over them, then sweat when brought in? Oil seems unavoidable.
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#3187926 - 01/23/19 10:25 PM Re: Understanding Pressure [Re: orkan]
Rock Knocker Online
Die Hard Member III

Registered: 12/29/11
Posts: 3061
Loc: Buffalo, MN
Originally Posted By: Flesh Eater

My question about the oil is how do you deal with rifles that get ice all over them, then sweat when brought in? Oil seems unavoidable.


When I get home from hunting in the cold, -15 to -20 at times. I ether leave the gun in the case until it's all at room temp or I take the gun out, dang thing freezes solid, literally, but field strip the gun as much as I can and place the parts over some of my furnace vents and that warms it up and drys it off pretty quick. Plus not having enough lube for it all to be flowing around helps also.

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#3187997 - 01/24/19 09:23 AM Re: Understanding Pressure [Re: Rock Knocker]
Flesh Eater Offline
Die Hard Member

Registered: 03/09/17
Posts: 665
Loc: 2D Pennsylvania
Originally Posted By: Rock Knocker
Originally Posted By: Flesh Eater

My question about the oil is how do you deal with rifles that get ice all over them, then sweat when brought in? Oil seems unavoidable.


When I get home from hunting in the cold, -15 to -20 at times. I ether leave the gun in the case until it's all at room temp or I take the gun out, dang thing freezes solid, literally, but field strip the gun as much as I can and place the parts over some of my furnace vents and that warms it up and drys it off pretty quick. Plus not having enough lube for it all to be flowing around helps also.


I've noticed my rifles seemingly dry up within an hour, but they sweat like crazy during the process. I assume if it's sweating on the outside of the barrel, it has to be sweating inside, right?

Do you oil your chamber at all? Would oiling it, then wiping it with a dry rag, or dry swab create the same pressure issues as discussed, or is that usually caused by an excess of oil?
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#3211172 - 08/29/19 11:57 PM Re: Understanding Pressure [Re: orkan]
JMette Offline
Junior Member

Registered: 02/05/18
Posts: 45
Loc: illinois
Velocity =‘s pressure. That helps a lot if you know roughly where your rifle should be shooting.
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Jeremy Mette

-Shoot Straight... Shoot often-

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#3211173 - 08/30/19 12:00 AM Re: Understanding Pressure [Re: JMette]
orkan Offline
Die Hard Member II

Registered: 06/27/03
Posts: 1745
Loc: Western SD
Originally Posted By: JMette
Velocity =‘s pressure. That helps a lot if you know roughly where your rifle should be shooting.


To clarify, are you saying velocity is an indicator of pressure?

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#3211257 - 08/31/19 12:56 AM Re: Understanding Pressure [Re: orkan]
JMette Offline
Junior Member

Registered: 02/05/18
Posts: 45
Loc: illinois
It could be. It’s the closest thing we have to measuring pressure. Nothing is the same in reloading. Everything is different and has variables. But if a safe pressure in a manual states a given FPS with a certain grain. It may take your rifle 1 grain more powder to achieve them same results or it may take your rifle 1/2 grain less. If you’ve got a loose barrel you won’t have pressures therefore you won’t have the velocities. If you’ve got a tight barrel you’ll have increased pressure and therefore you’ll get an increase in velocity with a lower powder charge

Hope makes sense.
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Jeremy Mette

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#3211258 - 08/31/19 01:00 AM Re: Understanding Pressure [Re: orkan]
JMette Offline
Junior Member

Registered: 02/05/18
Posts: 45
Loc: illinois
So essentially, yes velocity = pressure. Higher the pressure the more the velocity. Lower the pressure the lower the velocity. Only thing we’ve got to measure pressure is to judge by book velocity. Primer crater, head swipes, flatten primmer, can all show false pressures. And no signs doesn’t necessarily mean no high pressure either.
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Jeremy Mette

-Shoot Straight... Shoot often-

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#3211275 - 08/31/19 10:48 AM Re: Understanding Pressure [Re: JMette]
Bob_Atl Online
Die Hard Member III

Registered: 01/09/15
Posts: 2068
Loc: in the field, or not..
An old thread !

Need to be careful on the oversimplification of MUZ-V == PSI.

To illustrate, some powders will give a spike of pressure, above max PSI,
while other powders will give a safe smoothed mound of pressure for same MUZ-V.

A handy tool to see examples of estimated pressure curve shape is Quickload.
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#3211390 - 09/01/19 09:49 PM Re: Understanding Pressure [Re: Bob_Atl]
JMette Offline
Junior Member

Registered: 02/05/18
Posts: 45
Loc: illinois
I use quickload frequently. It’s a broad analysis about velocity but it’s true mostly to an extent.
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Jeremy Mette

-Shoot Straight... Shoot often-

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#3211503 - 09/03/19 01:13 PM Re: Understanding Pressure [Re: orkan]
orkan Offline
Die Hard Member II

Registered: 06/27/03
Posts: 1745
Loc: Western SD
JMette, I can not agree with your assessments here. Velocity is a result, and while some correlation exists, correlation does not imply or equal causation.

Especially in this case, because as Bob Atl said, pressure is pressure, and is not velocity specific in any instance. This is easily evidenced by the same loads being able to produce 100fps more or 100fps less in different barrels. So while velocity will be a metric for the median, to either side of the median is danger.


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#3213547 - 09/29/19 12:59 PM Re: Understanding Pressure [Re: orkan]
Don Fischer Offline
Seasoned Member

Registered: 12/19/09
Posts: 491
Loc: Antelope, Ore
Every thing you need to now about pressure. To much can blow up any rifle and do a lot of damage to you. Doesn't matter what the pressure is as the overwhelming majority of us have no means to measure it. That mean's pressure is just a number! What is important is to learn to recognize pressure sign's and how to avoid them. Then suddenly the number means nothing anymore because you'll never know what your getting in the first place. What you need to know is how to recognize dangerous pressure when you see it!


Edited by Don Fischer (09/29/19 01:00 PM)

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