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The first sign of excessive pressure is...

 
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  #8  
Old 05-28-2009, 04:22 PM
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Re: The first sign of excessive pressure is...

I am with AJ for the most part here.

I shoot most of my rounds over a chrony and ALL of my developmental loads over a chrony. The first thing I see before even lifting the bolt is the velocity reading. Most of the time I can predict whether or not the bolt will be sticky.

There are times however that I have pressure signs at lower than expected velocities and absolutly NO pressure signs at higher than expected velocities. It all depends on the primers, bullets, barrel quality, chamber demensions, twist, barrel length, how far off the lands you are AND whether or not all of these and more factors like the burn rate of the powder youre feeding it.

Pressure curves are also another complicated issue. You can still have HIGH pressure without pressure signs.

For me, I stop the ladder test as soon as I feel an abnormal bolt lift. It doesnt have to be sticky, just abnormal. Then I look for ejector marks, cratered primers and flattened primers. I pay no attention to the case head. Another BIG sign is loose primer pockets. Not neccesarily after many firings but if after one or 2 firings you dont have any resistance when seating a primer, it is time to back way the heck off. If I have even one sign, I stop and back off to the next charge weight below the last and I use that as a reference as my "max" load. Then I usually pick the most accurate load from the session below that one for "breathing room". In some cases, I will use a lower charge than max for most of my shooting and hunting but a max load where I know temps will be well under the mark when I developed the loads provided the accuracy is good at max. Most of the time it isnt.
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Originally Posted by Broz View Post
Please just answer one very simple question. Why would anyone shooting long range load a low BC , low SD 168 gr offering in a 300 win???????

My answer to this is. The only reason is to make the 7 RM look good. There is no other reason.

Jeff.
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  #9  
Old 05-28-2009, 08:20 PM
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Re: The first sign of excessive pressure is...

AJ and Michele seem to have developed a good process. My process is quite similar but depends on the chamber.

I've passed on the primer flattening though it is a bit of an indicator of things to come.

The shiny extractor mark is an indicator that says I've gone to far. I don't think the cartridge can 'fire' straight with the bump on one side.

On my REM 721 if there is the slightest of clicks as the bolt handle reached the top of its movement is the indicator that I use on that rifle. Any more powder than that needs one tap very firm tap to the rear by the hand to extract the case the first short amount.

I hate an early discard of brass which determines my working velocities.

Also, the RSI lab is a neat tool for factory cartridges where ball park pressures are published. Between the RSI and a good chrono you have it pretty much nailed.

On a wild cat it takes a little more shooting to determine an max pressure goal.
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Old 05-28-2009, 08:48 PM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by AJ Peacock View Post
He discusses both measuring difficulties as well as brass hardening in the article. I was very impressed with the article and it changed the way I did things. I'll be interested to find out what your impression of the information is.

Take care,
AJ

the article is very informative . it sure gives me more to think about . I feel like the rug was pulled out from under me . LOL I have noticed that it is hard to measure tenths on the case head , you have to be really on your game . I made a little block of wood to hold the case so I had both hands free .
I don't want to hijack the thread but this is what the original guy was asking and this info should or could help him too . you said you look at velocity as your primary pressure indicator , and I see your point of view . I've been playing with a 300 wby so it's still fresh in my head , and I have all my notes yet . I'm using a nosler ballistic tip 180 grain , with H1000 powder . my Nosler book says that starting load is 85.0 @ 3012 fps , and max load is 89.0 @ 3146 fps . I've found a node at 87.8 that shoots about .5" @100, and good extreme spread . it shows nice pressure signs . primer looks good . I'm using winchester mag primer ,I can get them easier . bolt works good . case head expansion is about .0003 . I use a chrony beta ,but my velocity is 3170 fps . by your method this load is too hot , because I have exceeded the book max velocity with a lesser amount of powder . am I correct ? I have not shot any of the brass cases enough to find the point of primer pocket stretch . thanks Jim

Last edited by jimbires; 05-28-2009 at 08:54 PM. Reason: spelling
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Old 05-28-2009, 08:59 PM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by jimbires View Post
the article is very informative . it sure gives me more to think about . I feel like the rug was pulled out from under me . LOL I have noticed that it is hard to measure tenths on the case head , you have to be really on your game . I made a little block of wood to hold the case so I had both hands free .
I don't want to hijack the thread but this is what the original guy was asking and this info should or could help him too . you said you look at velocity as your primary pressure indicator , and I see your point of view . I've been playing with a 300 wby so it's still fresh in my head , and I have all my notes yet . I'm using a nosler ballistic tip 180 grain , with H1000 powder . my Nosler book says that starting load is 85.0 @ 3012 fps , and max load is 89.0 @ 3146 fps . I've found a node at 87.8 that shoots about .5" @100, and good extreme spread . it shows nice pressure signs . primer looks good . I'm using winchester mag primer ,I can get them easier . bolt works good . case head expansion is about .0003 . I use a chrony beta ,but my velocity is 3170 fps . by your method this load is too hot , because I have exceeded the book max velocity with a lesser amount of powder . am I correct ? I have not shot any of the brass cases enough to find the point of primer pocket streatch . thanks Jim
I had a Chrony Beta that was consistently 2%-3% too fast. It consistently read 2-3% higher than Quickload estimated. When I changed to a CED M2, my velocities immediately started matching within 1% or closer to the estimates!

AJ
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  #12  
Old 05-28-2009, 09:27 PM
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Re: The first sign of excessive pressure is...

"
The first sign of excessive pressure is...
...flattened primers? Then ejector marks? Then sticky bolt?"

Those are the usual major signs but they don't give us the courtesy of showing up in predictable sequence. So...we just check for them all and note it when one shows up. What we do with that note depends a whole lot on how smart we are.
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  #13  
Old 05-28-2009, 11:53 PM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by AJ Peacock View Post
Jim,

In the past, I also used visual inpection of the brass, case head measurement and bolt lift/extraction as pressure signs. A couple years ago, I read an article about pressure and it changed my entire perspective on pressure/velocity and pressure signs. The author shows that from a statistical perspective, throwing a dart at a wall is about as good to indicate pressure as case head expansion is.

Here is a link to the paper.
http://www.shootingsoftware.com/ftp/...%2019%2004.pdf

I still monitor my brass and extraction, but I rely more on velocity. As long as I'm using an appropriate powder/bullet combination for the rifle, with published loads to compare velocities with; I trust the velocity I'm getting is a very good indicator that I am in a safe zone.
Wow.

A lot of great info here. Since my load is roughly 50 fps less than what Berger calls for and I am 1.6 gr hotter than their max load any thoughts on how much higher I can go?

Berger calls for 66.4 gr of Retumbo yielding 2849 fps. I just checked my load data and I am at 68.0 gr of Retumbo getting right around 2800 fps. I worked up from 65 grains and the groups keep tightening up as the load gets hotter.

Thanks to all who replied.
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  #14  
Old 05-29-2009, 12:15 AM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by buckbrush View Post
Wow.

A lot of great info here. Since my load is roughly 50 fps less than what Berger calls for and I am 1.6 gr hotter than their max load any thoughts on how much higher I can go?

Berger calls for 66.4 gr of Retumbo yielding 2849 fps. I just checked my load data and I am at 68.0 gr of Retumbo getting right around 2800 fps. I worked up from 65 grains and the groups keep tightening up as the load gets hotter.

Thanks to all who replied.
I am very interested in your findings. I am working on a 7 mag too. When I used Berger's max data (I was actually at 66.5 gr rather than 66.4 gr of Retumbo) I was 100 fps lower than what they claim. I too had no pressure signs and am using CCI 250 primers.
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