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I need help with pressure problems

 
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  #15  
Old 05-08-2012, 08:09 PM
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Re: I need help with pressure problems

Well there are 'pressure signs' that typically add up to mean 'pressure problems', or not.
If there actually is a pressure problem, you can directly measure it, as it is causing something -that is a problem. It is usually very obvious with multiple signs.

What is your problem?
Ejector marks?
In itself, that is neither a pressure problem, nor pressure causing a problem. Without other pressure signs it would more likely mean boltface issue, ejector issue, headspace issue, or chamber/die/poor plan..

You said you had 6thou HS clearance between what? Did you mean 6thou difference between new and fired brass? If so, this is excess headspace to be running full pressure loads with, and not a pressure, bolt, brass, or chamber problem.

Was there also difficulty in extraction seen as cases 'popping' out in the last bit of bolt turn(bolt click)? If so you can measure the cause near the webs. If not, there is probably not a pressure or brass problem.

I see a small bit of cratering around the firing pin, but can't tell if the primers are flattened. If not flattened, then this would be more of pin fitting than pressure sign.

It's good to watch for these and more(like cracks, thinning, loosening pockets). You should fireform new cases at slightly reduced load and get a baseline, with measurements, of what your chamber is taking brass to. With this it's easy to see what problems if any really are.
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  #16  
Old 05-08-2012, 10:49 PM
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Re: I need help with pressure problems

OK, so i see your point.

My first question about what you said is that .006 is to much headspace and yet my 300WM starts out with .020 headspace. Now it could be that a belted mag is headspaced off the belt so this is not an apples to apples comparison.

Im still not understanding what "the web" is...

there is no visible flattening of the primers.

I have some 123 Amax's and I will load a few of them down where there should be no issues at all.
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Last edited by AtownBcat; 05-08-2012 at 11:25 PM.
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  #17  
Old 05-09-2012, 04:09 AM
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Re: I need help with pressure problems

Quote:
Originally Posted by Mikecr View Post

What is your problem?
Ejector marks?
In itself, that is neither a pressure problem, nor pressure causing a problem. Without other pressure signs it would more likely mean boltface issue, ejector issue, headspace issue, or chamber/die/poor plan..
.
Mikecr could you explain the theroy behind the above causing brass to flow into the extractor.Excesive headspace I can understand although I wouldnt have thought .006 would have been significant given the 6.5x47 lapua brass and the very low velocity?
Cheers
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  #18  
Old 05-09-2012, 07:37 AM
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Re: I need help with pressure problems

my guess would be that you have a tight custom chamber and might require neck turned brass and bushing dies to resize to fit chamber.

just a guess
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  #19  
Old 05-09-2012, 07:48 AM
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Re: I need help with pressure problems

Yawn extractors and ejectors are different things, applying differently, to different casehead areas.
All I see in the pic is ejector marks, possibly caused by a weak ejector spring combined with excess headspace. This, given no other pressure signs.
I don't see any extractor marks, or flow. By the time you actually get extractor flow, you'd have a bunch of other signs as well.

AtownBcat
'Near the webs' by my definition is first NOT casehead expansion(CHE), or pressure ring expansion(PRE) points as horribly defined in the past. These stemmed from hopeless attempts to define actual pressure in the field. But because of the gamut of cartridge designs and situation variances, there is no defining of actual pressure via cartridge measurements alone.
I measure at a point forward of the webs that would represent the tangency(seamless transition) of web thickness to body thickness in a new case.
This is often also the point of thinning(a ring) with stretching cases. It can be seen as a line from dull brass above to shiny below. What's happening here to form that visible line in the sand is thicker web brass not expanding as much as body brass. So you have a point that represents the very widest point on the body as fireformed.

After I've fireformed cases(while determining best bullet seating), and before working up loads, I do a pressure test across a chrono & calibrate my QuickLoad file for the cartridge/barrel. I do this to find MY MAX, which I'll never go past again, and I let QL tell me what that pressure is based on the velocity-vs-load.
MY MAX is MY PROBLEM pressure, and is the point where extraction is sticky from well designed/fireformed/non-FL sized cases. This is typically calculated as ~57-65Kpsi, which is at or near SAAMI max, which is lower than some run, but high enough for me. I get no other pressure signs with this, and it holds from powder to powder provided my QL powder files are calibrated to lot.

For this testing I use simple calipers slid down the body to widest point. I don't mess with a blade mic & set datum because the actual datum(webline) can change from case to case. Also 0.0005 in resolution is good enough for the test.
As I go up in charge, I'll see the webline grow and settle at some point through several increases. This is where brass is expanding to the expanded chamber, and then springing back more than the chamber is springing back(allowing easy extraction). As I continue to go up in charge I will eventually measure a step change(from settled) of .0005. This represents brass yielding that is no longer allowing it's springback to clear the chamber. Sticky extraction, MY MAX..
This has held as valuable test criteria so far from 223 to WSSM.

So given that your extraction is not sticky, and having no other real pressure signs, and running known reduced loads, you do not have a pressure problem, or a brass problem.
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  #20  
Old 05-09-2012, 09:51 AM
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Re: I need help with pressure problems

Seems everybody else has pretty well covered everything, so I'll throw this out there. It may or may not explain a few things for you, unfortunately the only way for you to find out for sure is to spend the $ for this system, but the read alone was eye opening for me.
RSI - PressureTrace
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  #21  
Old 05-09-2012, 04:26 PM
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Re: I need help with pressure problems

Yes sorry of course Ejector is what I was refering to as the pictures show,my fingers dont always listen to my brain when I typing. But Im still at a little confused here.The case head shows a protrusion of brass where it apears to have flowed into the ejector cavity thats has been wiped off as the bolt was turned. So if how dose a weak ejector spring make brass flow? or a strong one prevent it if thats the case.Yes headspace maybe but the original poster has measured it at .006. and 6.5x47 lapua brass isnt soft by any stretch.?
Just trying to get my head aroud what your saying maybe happening here
cheers
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