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Got a question about flattening primers . This may have been asked before and probably has , however , when working up a load and looking for signs of pressure , i generally begin by looking for flattened primers and "sticky bolt lift" . However question is , when looking at a manual , how far does the book back down after pressure signs ? I have a couple of wildcats and i load for several others , and when comparing to others I'd kinda like a reference point . 1 grain under , 2 grains under ??? Not necessarily looking for the accuracy node just how the book figures max other than a pressure gauge !

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How much to back off depends on the cartridge size and the type of powder.Small cases like 223 a few tenths of a grain can make a big difference.In a larger case like a 300 Win Mag,.5grs or 1.0grs or more may be the amount you want to back off.The type of powder your using makes a big difference in the amount.Lets say the max load is 74.0grs of IMR 4350 and in the same rifle the max load was 79.0grs of Reloader 22.You would probably back off 1.0grs with the IMR 4350 and back off 1.5grs of the Reloader 22.These are just examples.


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Originally Posted by Sagerunner
Got a question about flattening primers . This may have been asked before and probably has , however , when working up a load and looking for signs of pressure , i generally begin by looking for flattened primers and "sticky bolt lift" . However question is , when looking at a manual , how far does the book back down after pressure signs ? I have a couple of wildcats and i load for several others , and when comparing to others I'd kinda like a reference point . 1 grain under , 2 grains under ??? Not necessarily looking for the accuracy node just how the book figures max other than a pressure gauge !


Reading pressure signs such as flattened primer is very imprecise. The best way is to chronograph and use the velocity as your guage.



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The “book” loads are determined by using test barrels and strain gauges. They don’t load up until they see pressure signs and then back down to determine max. They fire hundreds of rounds and actually measure the pressures. SAAMI has determined the max pressure, so when they reach that pressure, that is the max.

That being said, each barrel and chamber are different, which is why every book recommends backing down by 10% and working up slowly.

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Thanks for the info , i have a couple wildcats . One is a 338/300 win improved and it's accuracy node was just under ( 1.3 grains ) under first pressure signs . That's really the one I'm interested the most in . The other is a 260ai and it really doesn't care what you feed it or how hot or cold it is , it shoots everything I've fed it so far very well !

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How is your brass holding up?

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Originally Posted by jwp475
Originally Posted by Sagerunner
Got a question about flattening primers . This may have been asked before and probably has , however , when working up a load and looking for signs of pressure , i generally begin by looking for flattened primers and "sticky bolt lift" . However question is , when looking at a manual , how far does the book back down after pressure signs ? I have a couple of wildcats and i load for several others , and when comparing to others I'd kinda like a reference point . 1 grain under , 2 grains under ??? Not necessarily looking for the accuracy node just how the book figures max other than a pressure gauge !


Reading pressure signs such as flattened primer is very imprecise. The best way is to chronograph and use the velocity as your guage.
^^^^^THIS

There is great variation in primer flatness at the same pressure, even just using primers from a single lot.

The other pressure signs tend to kick in at around 70 KPSI. In a 308 range case, a grain of powder is very roughly 2500 PSI. So if you're getting those signs, you probably want to back down 3-4 grains.

Also a very approximate statement: In good brass, primers start falling out at around 80 KPSI. If you get that, thank your lucky stars that you still have all your body parts, pull down your loads, sell your firearms, and take up photography.

Im constantly amused by people who think they can second guess a well equipped laboratory by firing a few rounds and looking at the primers or measuring the case head.

Last edited by denton; 10/06/22.

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Get a chronograph before you have a bad situation.

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Most of what i have to say has been said, saving me lots of typing.
1) Primer appearance means very little. There is great variance in the hardness of individual primer cups. I just ran some 30 year-old WLR in some 30-06 loads that came out flat as a pancake, but the chronograph indicated relatively benign pressure. Primer cratering is more often the result of slop between the firing pin and the hole it slides through than high pressure. I have a (way) sub-MOA Christensen Mesa that always craters reasonable loads, regardless of pressure. Same for a pair of Rem M7 Predators in .243 and .223. The FN Mauser that flattened those old WLRs like a pancake had a perfectly fitted firing pin and absolutely zero cratering.
2) Sticky bolt lift, maybe accompanied by ejector marks, is usually a reliable indication of excess pressure. and in these "usually" situations you are likely pushing 70K PSI. But there are other things, like burrs around the ejector slot or plunger hole, or a rough chamber, that might sometimes show those signs at lesser pressures.
3) While case head expansion is worthless to determine absolute pressure, I have found it to be a very useful indication of relative pressure within a single lot of brass. And it's a good predictor of how long your brass is going to last. Less than .0005" CHE on virgin brass is a pretty good indicator of long brass life. And it should go without saying that you don't do CHE with a caliper. You need a micrometer, preferably a blade mic so you don't have to file case rims on unbelted or non-rebated cases, and the ability to use it to read measurements to .0001"
4) Best for Last - The Chrono is your friend. For a given load (and yes, there are other factors) speed is approximately equal to pressure. If the book max got 2975 FPS with powder x and bullet y, if you load your rifle (with the same length barrel!) to the same speed with powder x and bullet y, it might take one or two grains more or less than the book lists. But if you stop there, you are very likely in a safe place. And for that matter, different lots of the same powder could require the same consideration. If your extra-special custom load beats the book by 100 FPS, you are pretty reliably well over SAAMI max.
5) Which might not matter - There is nothing about necking down the 30-06 case (60K PSI max) by .031 to .277 that magically makes 65K PSI safe in your rifle. 65K is either safe or it's not in a particular action and that's why the .270 Win is a really bad candidate to hot-rod, while the 30-06 has a fair bit of "head room". But if either of them shows hard bolt lift or ejector marks its time to back down.

And I said the other respondents saved me a lot of typing. God help us if they'd not written first...
Cheers,
Rex

Last edited by TRexF16; 10/06/22.
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Buy a chronograph.


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Originally Posted by TRexF16
Most of what i have to say has been said, saving me lots of typing.
1) Primer appearance means very little. There is great variance in the hardness of individual primer cups. I just ran some 30 year-old WLR in some 30-06 loads that came out flat as a pancake, but the chronograph indicated relatively benign pressure. Primer cratering is more often the result of slop between the firing pin and the hole it slides through than high pressure. I have a (way) sub-MOA Christensen Mesa that always craters reasonable loads, regardless of pressure. Same for a pair of Rem M7 Predators in .243 and .223. The FN Mauser that flattened those old WLRs like a pancake had a perfectly fitted firing pin and absolutely zero cratering.
2) Sticky bolt lift, maybe accompanied by ejector marks, is usually a reliable indication of excess pressure. and in these "usually" situations you are likely pushing 70K PSI. But there are other things, like burrs around the ejector slot or plunger hole, or a rough chamber, that might sometimes show those signs at lesser pressures.
3) While case head expansion is worthless to determine absolute pressure, I have found it to be a very useful indication of relative pressure within a single lot of brass. And it's a good predictor of how long your brass is going to last. Less than .0005" CHE on virgin brass is a pretty good indicator of long brass life. And it should go without saying that you don't do CHE with a caliper. You need a micrometer, preferably a blade mic so you don't have to file case rims on unbelted or non-rebated cases, and the ability to use it to read measurements to .0001"
4) Best for Last - The Chrono is your friend. For a given load (and yes, there are other factors) speed is approximately equal to pressure. If the book max got 2975 FPS with powder x and bullet y, if you load your rifle (with the same length barrel!) to the same speed with powder x and bullet y, it might take one or two grains more or less than the book lists. But if you stop there, you are very likely in a safe place. And for that matter, different lots of the same powder could require the same consideration. If your extra-special custom load beats the book by 100 FPS, you are pretty reliably well over SAAMI max.
5) Which might not matter - There is nothing about necking down the 30-06 case (60K PSI max) by .031 to .277 that magically makes 65K PSI safe in your rifle. 65K is either safe or it's not in a particular action and that's why the .270 Win is a really bad candidate to hot-rod, while the 30-06 has a fair bit of "head room". But if either of them shows hard bolt lift or ejector marks its time to back down.

And I said the other respondents saved me a lot of typing. God help us if they'd not written first...
Cheers,
Rex

Summed up: Get a chronograph.


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Without a chronograph you have no idea what your velocity is running.It's a really good tool and well worth the money spent.


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And for a more thorough explanation about primer flattening, read this article:

https://www.24hourcampfire.com/ubbt...3673133/1/march-column-primer-flattening


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Everything Denton and TRex said…….


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Got a chronograph. Not sure how that helps when you have a wildcat and no data ? As far as i know me and a friend are the only 2 made rifles out there . As for the rest , i sure do appreciate the info . I had to go back and look at notes . The first extractor marks were the very first sign. But the primer had also just started to flatten, just a little. Backed down from there. It's a big round so don't want to "lose" something I'll miss later !

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If you have wildcats and no source of reliable pressure data, then your situation is a bit tricky.

I think that your least unreliable easy approach is to use QuickLoad. If you enter actual case water capacity, brass length, bullet length, etc., instead of taking the defaults, it is likely to get you within a percent or so.

The best approach is to get a PressureTrace. A careful user can produce high quality data with that device.

Last edited by denton; 10/07/22.

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I concur with Denton.

You might find a factory cartridge with nearly the same case capacity etc and that would be a valuable reference.


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Well , i started with mild 338 win mag to start and then started with hot 338 win mag crossed with 240 grain 300 win mag. Somewhere in the 78 grains of 4831sc and worked up . Got just under 86 to get sticky bolt lift then backed down to 84.

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And how is your brass holding up at 84 grain level?

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You could easily us Mule Deer's "Rules" to find a nice base line to keep yourself in one piece!


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