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Old September 16, 2018, 10:18 PM   #1
Bigdaddysmith
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Short barrel handguns showing less pressure signs.

I've been using 6.2gr CFE Pistol powder for 45acp.
I'm using acme coated 230gr lrn bullets. Oal 1.2. Federal brass.
Winchester lrg pistol primers.

In my XD 45 Tactical I'm avg 946fps slight pressure signs on primer. Aka very slight flattening.

Now in my Shield 45 I'm getting an avg of 858 fps. No pressure signs. Same load.

Am I wrong to assume that shorter barrels are not getting full burn thus lowering pressure?

If so should I raise the powder 0.1gr until I see signs of pressure just to see how high I can get velocity out of my short barrel?

Has anyone had experience in this already?
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Old September 16, 2018, 11:19 PM   #2
74A95
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Peak chamber pressure occurs before the bullet has moved one inch. The differences you see in pressure signs are likely just due to different barrels. Not all barrels react the same to the same ammo.

Reading pressure signs via primer flattening, etc is not an exact science, and could lead you to trouble. Trust, and follow, the data in your loading manual.
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Old September 17, 2018, 01:34 AM   #3
Bigdaddysmith
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Okay thank you for the good information.
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Old September 17, 2018, 05:22 AM   #4
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I'll second the thought that reading "pressure signs" as a green light to add a bit more powder is not a good practice.

Primer cups vary,by brand and application. I don't think CCI or Federal calibrate the cups as pressure indicators.

I confess,I do look at my primers.I'm looking for caution lights and stop lights.

Something to consider.Most of the "signs" apply to centerfire rifles of bolt action strength operating safely at 50,000 to 65,000 psi.

Its a bad plan to apply those same signs to an 1873 Win lever action or a 30-40 Krag with a single locking lug and 1898 steel.

You read flattened primers and you may get a bolt through your cheekbone.

I'm not going tolook up SAAMI pressures right now,but a 45 ACP operates at about 20,000 psi.The same primer might be used in another cartridge at 36,000 psi. Lets say they flatten ,in this alternate cartridge,at 38,000 psi.

What does that tell you about flattening primers in a 45?

Use the load manuals.

With identical pressure,its to be expected that velocity will be lower.

A 1/8 mile dragstrip will yield lower top speeds than a 1/4 mile dragstrip with the same engine. Acceleration,time,distance....

Last edited by HiBC; September 17, 2018 at 05:29 AM.
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Old September 17, 2018, 03:28 PM   #5
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Quote:
Am I wrong to assume that shorter barrels are not getting full burn thus lowering pressure?
That is correct: you are wrong to assume so.

Peak pressure occurs within the first milliseconds of detonation - before the bullet leaves the barrel; no matter how short.

That said, I don't have an explanation of why the primers look different between the two guns. Maybe differences in their breech faces??

Anyway, reading primers for pressure signs is a bit like reading tea leaves - and probably less accurate. I can however, see the difference in primer flattening between nominal pressure and high pressure loadings in 45 ACP. Any detail beyond that is impossible. And small primers are even less telling.
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Old September 17, 2018, 05:53 PM   #6
reynolds357
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Reading primers is a bad idea. The same primer is used in a 45acp and a 10mm auto. Max Saami pressure of a 10mm is almost double that of a 45cap. If you are flattening the same primer in a .45 that goes in a 10, what does that tell you?
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Old September 18, 2018, 12:50 PM   #7
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"...not getting full burn..." That big muzzle/cylinder gap flash is the powder burning.
6.2 grains(20,100 PSI) of CFE Pistol is already the MAX Load for a cast 230. No raising the powder by anything.
You work up to that or just pick it?
You do not want to see any signs of pressure, but you do not load to get 'em either.
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Old September 20, 2018, 11:27 AM   #8
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Primer signs...

Quote:
Am I wrong to assume that shorter barrels are not getting full burn thus lowering pressure?
Yes, this is an incorrect assumption.

Quote:
If so should I raise the powder 0.1gr until I see signs of pressure just to see how high I can get velocity out of my short barrel?
Nichts! Nein!, und HELL NO!!!!!


Quote:
I confess,I do look at my primers.I'm looking for caution lights and stop lights.
So do I.

Quote:
Something to consider.Most of the "signs" apply to centerfire rifles of bolt action strength operating safely at 50,000 to 65,000 psi.

Its a bad plan to apply those same signs to an 1873 Win lever action or a 30-40 Krag with a single locking lug and 1898 steel.
I disagree. It's a bad plan to disregard pressure signs, and much more important in some guns, than others.

Quote:
You read flattened primers and you may get a bolt through your cheekbone.
You read flattened primers WRONG and you may get a bolt in the face...

Quote:
Reading primers is a bad idea.
again, reading primers wrong (making incorrect conclusions) is a bad idea.

Quote:
The same primer is used in a 45acp and a 10mm auto. Max Saami pressure of a 10mm is almost double that of a 45cap. If you are flattening the same primer in a .45 that goes in a 10, what does that tell you?
It tells me not to consider different things as identical, because they share some common components.

OK, yes reading primer signs is like reading tea leaves. The only consistent and reliable information tea leaves give you is that somebody drank the tea.

The only thing flattened or cratered primers tell you with absolute certainty is that something undesired is going on. The most likely cause is higher than expected pressure. But its not the only possible cause.

Primer pressure signs are not a calibrated thing. And, they cannot be, so don't think of them like that. There is no "primer A flattens at 32K psi.." because while it might, it also might not.

EVERY GUN AND AMMO COMBINATION CAN BE DIFFERENT.
There are a huge number of factors about the gun, the ammo, and their fit together that affect pressure signs on primers (and cases).

The exact same ammo that craters primers in gun A may not crater primers in gun B. And it may be well within the SAAMI listed specs as "safe". Or it could be outside them. The primer won't tell you which. All it tells you is "I'm not happy about something".

When you get a pressure sign, like a flattened primer it doesn't matter (much) what the actual pressure number is, what matters is that for that particular gun, with that specific combination of load components, you go no further.

What the "book" data says a max load is, is the max load they reached with the firearm and components they tested. While its usually very similar, the safe max load in your gun or mine with our different components can be significantly different.
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Old September 20, 2018, 03:05 PM   #9
HiBC
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Quote:
Something to consider.Most of the "signs" apply to centerfire rifles of bolt action strength operating safely at 50,000 to 65,000 psi.

Its a bad plan to apply those same signs to an 1873 Win lever action or a 30-40 Krag with a single locking lug and 1898 steel.
We agree that its a bad idea to ignore pressure signs.The point I was trying to make...and IMO,its an important one,isabout a LACK of "pressure signs " being read as a "green light"

We agree primers are not calibrated pressure indicators.But suppose a given rifle primer ,in combination with other factors,flattens at about 68,000 psi.

If you are shooting a Krag that we want to keep under 40k psi,a lack of a flattened primer is not a green light.We don't want 68,000 in a Krag.

I say this because ill informed handloaders may have an idea of "pressure signs" applicable to firearms much stronger than what they are shooting.

FWIW,I recall a Marlin 30-30 with excessive headspace that would show high,backed out primers at lower pressure loads. When pressure goes up enough to stretch the case head back to the bolt face,those primers look REALLY flattened at reasonable pressures.

As you said,signs are like tea leaves
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Old September 20, 2018, 04:37 PM   #10
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Some of the flattest primers I have ever encountered have come from 'factory' ammo...

Winchester white box 240gr .44 mag come to mind...

That was back in the early 90's though, so I have no idea about current factory ammo of any flavor...
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Old September 20, 2018, 05:15 PM   #11
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Quote:
That is correct: you are wrong to assume so.

Peak pressure occurs within the first milliseconds of detonation - before the bullet leaves the barrel; no matter how short.
I shoot some of the hottest loads available in most of the common calibers and I don't think I've ever seen what I would consider a flattened primer. I use only Winchester primers and some brands are softer than that.

But I have always been under the assumption that if I flatten a primmer in any of my magnums I've already damaged one of my revolvers. Like the others have said, pressure signs doesn't work the same in a handgun as it does in a rifle.
Just my opinion.
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Old September 21, 2018, 07:09 PM   #12
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It's complicated. For example, a 45 auto may run at lower pressure than a 10 mm, but if the 45's excess headspace is greater, the slower and lower pressure may let the primer back out to take up the excess headspace and then dwell there longer as the primer inflates and before the case head comes back to reseat it. In other words you may get more mushrooming in the ACP case resulting in greater appearance of flattening even though pressure is lower. But it still means the primer is at its limit in the 45 Auto with the chosen powder charge.
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Old September 24, 2018, 04:25 PM   #13
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Another thing that will lower pressure is the throat.
A gun with a generous (longer) throat will develop less pressure than one with a short throat .
Loads in the longer throated barrel will show no pressure signs, the same loads in the short throated might show signs of pressure.
Each gun is a law unto itself.....so many variables to consider, a load that's fine in one may not be in another, work loads up in each .
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