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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 Online
PM senior

Registered: 01/31/14
Posts: 5013
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 Offline
Die Hard Member with a vengeance

Registered: 02/12/15
Posts: 4141
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.
_________________________
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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Jeremy

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#2978329 - 07/20/16 06:43 AM Re: Understanding Pressure [Re: reaper4]
7887mm08 Offline
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.
_________________________
Longest kill shot to date, 620yds with a custom built 22-243 Win.

"In GOD We Trust"

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#2978339 - 07/20/16 08:38 AM Re: Understanding Pressure [Re: orkan]
mbaysinger89 Offline
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 Online
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. Online
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 Offline
PM senior

Registered: 01/08/03
Posts: 8402
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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