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  #1  
Old 05-31-2009, 10:50 PM
Mntngoat Mntngoat is offline
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Default Pressure whats aceptable??....

I think we are all aware of flattened primers as a sign of too much pressure. but what about measuring just in front of the case web? I have a few cases that were fire forming the primers are NOT especially flat the the web measures .003" larger on the fire formed case compared to a new case.

FWIW: it required a cleaning rod to get the case out of the chamber, it would not extract. Quickload said it was still well in the safe area of pressure for this case.


ML
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Last edited by Mntngoat; 05-31-2009 at 11:46 PM. Reason: Clarifications
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Old 05-31-2009, 11:11 PM
Oleman Oleman is offline
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Default Pressure

Every gun varies. Did the gun extract other shells after this one? What was your load? Do you have a chrongraphed MV for the load in question. Show us some primer pictures.
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Old 05-31-2009, 11:27 PM
scootertrash scootertrash is offline
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Quickload may have said safe for after fire forming, but did you measure H20 of the parent case? Also, did you chrono the powder to obtain the correct burn rate, or are you just using QL's default? I have seen powders 12% faster than QL's default.

Or...can it just be the chamber is big in that area?

Mike
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Old 05-31-2009, 11:44 PM
Mntngoat Mntngoat is offline
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wish I had the chrono with me. I'm pulling the bullets and starting over. It's only 30 rounds. Mike I do believe the parent case is a bit smaller and if I run it with parent case I could get into pressure real quick. Think I will load these at the range next time out.
New chamber so hoping it's not that big, the fact that it won't eject is an issue too.

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Old 06-01-2009, 12:02 AM
trotterlg trotterlg is offline
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Unless you are expanding the base, which will make loose primer pockets, I think this is just normal. Larry
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Old 06-01-2009, 02:12 AM
GLWenzl GLWenzl is offline
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I wonder if there is a scratch in the chamber for the sticky case…. Being .003 larger sounds bad to me no matter what the problem is… I would stop everything until was able to do a good inspection of the chamber and/or a chamber cast… To me QL is just a guide and I would be cautious about using it without some careful thought…. JMO
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Old 06-01-2009, 02:52 AM
Dan C Dan C is offline
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Mike, I believe flat primers are a very unreliable method of 'guessing' excessive pressure. It's more often an indication of more headspace than ideal.

Concerning head expansion, you must be very careful where the measurement is taken. It's only meaningful when taken before and after, in the exact same place, just ahead of the extractor groove. Not at the 'bulge', which is only an indication of chamber diameter. If your case truly expanded .003" at the head, the primer would have fallen out. But again, it's not real dependable or repeatable.

I prefer overall primer appearance along with case life when determining max load. You can tell when a primer has been subjected to really high pressure; it takes on the exact machine marks of the boltface, the firing pin indentation will have very defined edges, things like that. Finally, I use the primer pocket condition after multiple loadings when determining max load.

For example, when doing the initial workup with the 20 Killer Bee, I was doing my loading at the range. Slowly increasing powder charges and monitoring with the chronograph and watching all the usual signs, I reached an almost unbelievable 3864 fps with the 32 Vmax's. I then took a fired case and loaded and fired it an additional 10 times, neck sizing only. Although the case started to get a little tight chambering, the primer pocket stayed tight and the case was still in fine shape, just needing to have the shoulder bumped.

So that's sort of my rule of thumb. 10 shots with the same case without damaging it, and I consider that a safe load in my rifle. I'll normally back off from that and then start considering accuracy in fine tuning the load.

Regarding QL, I don't consider that a reliable indicator of pressure with these weird little cartridges. They are too far from 'standard' for QL to be of much use in my opinion. Various things can be adjusted to match existing loads, but that is sort of putting the cart before the horse.

Dan
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Old 06-01-2009, 03:05 AM
trotterlg trotterlg is offline
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How far ahead of the extractor groove are you measuring it? Larry
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Old 06-01-2009, 03:13 AM
Easy_E Easy_E is offline
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I hate to butt in on another guys post but the same question has been eating at me. I have flattened primers out of my .17 fireball with all brass . The gun is all stock chamber.
I thought it was my formed brass doing it buy after a chamber cast the clearance was about .003 . I shot factory , .221 to .17 fb and .223 to .17 fb brass with the same flattened primers. Some worse than others. Also the gun extracts with no problem.
Here's a pic....


http://img5.imageshack.us/img5/8803/dsc05526zjh.jpg
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  #10  
Old 06-01-2009, 03:32 AM
trotterlg trotterlg is offline
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Those primers are standing about .010 out of the case, only way to get that to happen is to have that much headspace. They are not that flat to me. Larry
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