Pressure signs vs velocity

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Don’t overthink this. We’re driving on a super-highway, not riding on a razor edge. MAP’s are established with a generous safety margin, and it’s really not pertinent to assume every equal integral of a pressure curve represents the exact same curve, nor that the same velocity (within our margin for error in measuring velocity) is an indicator of the exact same integral of the pressure curve. Ain’t non-linear math fun?

Here’s an example: two barrels from the same manufacturer with the same specs, reamed the exact same day on the exact same reamer, yielding two chambers within 5/10,000 in headspace and bolt-face-to-leade length. Both of these matching two other barrels from the same manufacturer a year prior, chambered to within the same standard by the same smith on the same frame. Using the same lot of bullets, same lot of powder, primers, and brass, and the same load - three of these barrels gave velocity within a handful of fps... all 4 produced signs of excessive pressure at the same charge weight and all 4 produced a velocity node within 1/10th of a grain.

But one barrel produced velocity ~80fps faster than the other 3...
 
murf said:
then maybe i misunderstood newton's third law of motion. chamber pressure is the force that is acting on the slide. more pressure means more force applied to the slide which means more slide velocity. more slide velocity means a more forceful case ejection. a more forceful case ejection means the case lands farther from the gun.
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It's a misunderstanding/misapplication of recoil force. Chamber pressure is not applied to the slide. Recoil force is.

Ejection distance is a function slide weight and various springs. In your example, it could be wrong to conclude that an ejection of distance X means you're overpressure compared to factory ammo. It could be a difference in the powder that the factory uses and what the handloader uses.

Recoil force is a function of bullet weight, bullet velocity, powder charge weight and gun weight. Chamber pressure is not involved. One can produce very high peak chamber pressure with a fast powder but not necessarily high velocity. Using a slow powder one can get lower peak chamber pressure but higher bullet speed. This will produce more recoil force.

murf said:
you can run these steps backward to understand that cases farther from the gun means more chamber pressure.
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Only if you're using the same powder. If not, all bets are off.
 
jmorris said:
How about not starting at “max”.
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Agree. This was a question pondered so that I could gain more knowledge.

Erief0g said:
As I consider working up some loads with my rmr mprs I plan to bump them up to decent speeds i wondered about pressure.
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This is what I plan to do. Work up some loads. In looking at my log book I've already made some RMR 124gr MPR"s that hit 1100 fps and plan to make some more with a different powder.

Just a knowledge based thread for me. Take a little bit of what y'all say, research it with reference publications, and come up with my best method to work up to my goal.

I don't want to be at max... I want to be at 1100fps with 124gr rmr mpr. Very very doable without hitting max or over with proper powder and load work up.

In all actuality it may be quite some time before I get there. Already have 6k 124 mw"s loaded and as far as jhp"s probably 700 of federal hst"s when the buying was good.
I'm currently working on load development for my cast 230 gr rnfp hitek coated 45acp rounds. Got my max oal and dies set up. Just need to do 15 each at a nice spread of charges.
Then I'll be doing the exact same thing for my 44 mag mold that I'm just breaking in.

Lots of discussion, lots of tweaking stuff, lots of casting... not a lot of shooting.
 
Varminterror said:
Don’t overthink this. We’re driving on a super-highway, not riding on a razor edge. MAP’s are established with a generous safety margin...
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A lot of folks don't seem to realize this. If a cartridge has a MAP of 60,000psi, the gun that chambers it is not gonna blow sky high at 65,000. Using the Linebaugh .45Colt data for example, the safety margin is 100%. That's a lot. It takes a huge screw up or a really dumb handloader to do anything that causes a problem, much less a catastrophic failure. Which is why worrying about pressure being different between guns and pressure barrels or even bullets of the same weight/size/construction but different brands, is a total waste of mental bandwidth.
 
BBarn said:
But consider data such as this:

For the 223, Hornady lists a max load of 24.9gr. of Varget behind the 60gr. Vmax bullet, using Win cases and primer. With that load they report a MV of ~3000fps in a 26" barrel. Hodgdon lists a max Varget load of 27gr. with the Hornady Vmax, with the same brass, and primer. Hodgdon reports a MV of 3159fps with their load.

Using your line of reasoning, there seems to be only two ways to reconcile this:

1) Hornady's data is for multiple bullets and the actual Vmax data is 2.1gr below max.

2) Hornady's data is limited to substantially less pressure than the Hodgdon data.

Are we to assume only one source is correct? And if so, which one?
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Looking at Hornady's latest PDF online, they do indeed report 3000 FPS with 24.9 grains of Varget. But they do not report either the pressure that they loaded to, or the barrel length they used. Hodgdon does report a 24" barrel and 51,900 CUP, which may be a typo. 51,900 CUP is just shy of 60,000 PSI, which would be permissible with a 5.56x45 load, but in excess of spec for 223.

I don't think you've made a case that there is a peak pressure discrepancy.
 
denton said:
I don't think you've made a case that there is a peak pressure discrepancy.
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In their Handbook of Reloading, Hornady says they generate data until max SAAMI pressures are reached. Yet, their max load is well below the Hodgdon data. You suggest there is no pressure discrepancy even though you also claim the same pressure will produce essentially the same MV if components and barrel length are the same. You can't have it both ways.

I guess these companies are just wasting resources supporting SAAMI, measuring pressures, and warning customers not to exceed their published data. We can just pick out a desired max muzzle velocity we find in a reloading book, adjust for any difference in barrel length, and add the specified powder until we reach our max muzzle velocity. At that point we'll be at max pressure because we have reached the correct muzzle velocity.
 
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fxvr5 said:
It's a misunderstanding/misapplication of recoil force. Chamber pressure is not applied to the slide. Recoil force is.

Ejection distance is a function slide weight and various springs. In your example, it could be wrong to conclude that an ejection of distance X means you're overpressure compared to factory ammo. It could be a difference in the powder that the factory uses and what the handloader uses.

Recoil force is a function of bullet weight, bullet velocity, powder charge weight and gun weight. Chamber pressure is not involved. One can produce very high peak chamber pressure with a fast powder but not necessarily high velocity. Using a slow powder one can get lower peak chamber pressure but higher bullet speed. This will produce more recoil force.



Only if you're using the same powder. If not, all bets are off.
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rather than sidetrack this thread, i will just disagree with your notion of "recoil force" and reiterate that one can judge relative chamber pressure by observing the case ejection distance.

murf
 
BiknSwans said:
Pressure and force are not the same. Force is pressure times area in this case. More pressure on the slide (actually force) does mean more velocity for the same recoil spring. Velocity of the slide is a function of the mass of the slide and the stiffness of the recoil spring. Using a stiffer recoil spring reduces the case ejection. Looking at how far the case is ejected is useless for pressure indications.

From this link on Enos, the post written by IDescribe, one of the signs of over pressure, maybe the best in my opinion, are that the velocity increase becomes non-linear with increases in charge.

https://forums.brianenos.com/topic/221357-how-do-you-use-a-chronograph-to-work-up-a-load/
first, pressure is force: https://en.wikipedia.org/wiki/Pressure

second, this only works for a specific gun. ejection distance info cannot be transfered to another gun. changing recoil springs makes for a different gun.

third, i didn't say anything about slide velocities, or case ejection, being linear.

so, case ejection distances are a good way to tell if your load is over max pressure.

murf
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murf said:
i will just disagree with your notion of "recoil force" and reiterate that one can judge relative chamber pressure by observing the case ejection distance.
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No you can't. One powder can have lower peak chamber pressure and more recoil force than a powder that produces higher peak chamber pressure. This isn't speculation, it's fact.

See figure 4 at the link below, for the 45 ACP and 38 Super No Compensator condition.
https://www.shootingtimes.com/editorial/compensators-pressure-gas/99170

Chamber pressure is not part of the formula that calculates recoil force.
https://en.wikipedia.org/wiki/Recoil

Different powders produce different amounts of recoil when pushing bullets to the same speed. In general, fast burning powders produce less velocity at peak chamber pressure than slow powders. You can see this in loading manuals. If you look at pushing the same bullet to the same speed with different gunpowders, slow powders require more powder weight, and this extra powder weight itself will produce more recoil force via the conservation of mass explained in the Wiki link. This difference is calculable and measurable.
https://www.shootingtimes.com/editorial/measure-relative-handgun-recoil/99442
 
BiknSwans said:
Pressure and force are not the same. Force is pressure times area in this case. More pressure on the slide (actually force) does mean more velocity for the same recoil spring. Velocity of the slide is a function of the mass of the slide and the stiffness of the recoil spring. Using a stiffer recoil spring reduces the case ejection. Looking at how far the case is ejected is useless for pressure indications.

From this link on Enos, the post written by IDescribe, one of the signs of over pressure, maybe the best in my opinion, are that the velocity increase becomes non-linear with increases in charge.

https://forums.brianenos.com/topic/221357-how-do-you-use-a-chronograph-to-work-up-a-load/
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Interesting posts by IDescribe in the link. I've never pushed pressure high enough to get major SD variations but it's nice to know what to look for when reading SD.
 
NMexJim said:
Interesting posts by IDescribe in the link. I've never pushed pressure high enough to get major SD variations but it's nice to know what to look for when reading SD.
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ID's post is speculation. "They are hypothetical and meant to show patterns. Actual numbers can differ dramatically."

ID does not show corresponding pressure data. If he/she does not have pressure data to support his/her claims, it's not helpful. It could be wrong. SDs could go in the other direction. That's why real pressure values are required, and for several powders. Same thing for the velocity claims. Velocity and pressure data is required.
 
one can judge relative chamber pressure by observing the case ejection distance.
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Like the peak pressure/velocity argument, that would require some other qualifying parameters to be true.

We all know with squib (very low peak pressure) the bullet won’t have much if any muzzle velocity and the case won’t go anywhere. However, there are also examples that show very high peak pressures also won’t have much muzzle velocity and leave cases in the chamber, at least what’s left of them.

008D5FBB-809C-4D56-B424-257A2EAD3A49.jpeg 4A807FA9-6D7D-4DBE-A410-157DF6D7683E.jpeg

That shows us definitively that peak pressure does not have a linear relationship with muzzle velocity (even in the same barrel with the same bullet). Generally easiest to see when one goes to extremes.
 
It’s also provable that many don’t, even if the bullet does have muzzle velocity over 0. As it’s also provable that extremely high.pressures might also have a case not remain in the chamber but some do, as above.
 
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fxvr5 said:
ID's post is speculation. "They are hypothetical and meant to show patterns. Actual numbers can differ dramatically."

ID does not show corresponding pressure data. If he/she does not have pressure data to support his/her claims, it's not helpful. It could be wrong. SDs could go in the other direction. That's why real pressure values are required, and for several powders. Same thing for the velocity claims. Velocity and pressure data is required.
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Yep, that's what he said as well as saying that he has enough experience that the data would be viable.

My first mental image of his data was a pressure spike would take the bell curve near straight up and narrow the curve shoulders and therefore the standard deviation would drop just as he has shown. At the time, I thought that reasonable. Your comment sent me back to the drawing board and interior ballistics. I'm still working through it all, but I don't see his posit a failure at this point. My ballistic books are packed up right now, but I'll get back if I find out different.
 
NMexJim said:
Yep, that's what he said as well as saying that he has enough experience that the data would be viable.

My first mental image of his data was a pressure spike would take the bell curve near straight up and narrow the curve shoulders and therefore the standard deviation would drop just as he has shown. At the time, I thought that reasonable. Your comment sent me back to the drawing board and interior ballistics. I'm still working through it all, but I don't see his posit a failure at this point. My ballistic books are packed up right now, but I'll get back if I find out different.
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His arguments require actual pressure measurements. If one does not have that, it's just speculation.

We don't know what his "experience" is. It might or might not pass a smell test. I'm not inclined to buy into that from some unknown poster on a forum. Regardless, it requires actually measuring pressure.
 
NMexJim said:
My ballistic books are packed up right now, but I'll get back if I find out different.
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Please do. I agreed with most of ID’s post with the exception of #2, SD. There are a lot of variables involved with reloading, and even a few with taking chrono measurements that can attribute to higher SDs. I can see if you had a test ladder set up and SDs were tracking and then one ladder had a 5-10X jump maybe something is off but it’d be hard to relate it to pressure.
I use my pistol SD numbers to give me some confidence when I’m at the chrono stage and randomly select 7 rounds from my production run I’m not going to be told “You’re shooting the match for fun, son...”.
 
For the benefit of those who do not believe that peak pressure predicts/drives muzzle velocity, with the same powder and bullet, I offer the following. I have done similar measurements for other cartridges, and they all come out looking like this:
148260.gif

In this case, peak pressure accounts for 99% of the variation in muzzle velocity, leaving only 1% to be explained by other other factors.
 
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It would be interesting to compare say the pressure curve obtained by only changing seating depth, leaving all other variables the same with the velocity curve.

656BEE91-20C5-4E4D-96F4-5DEA8A7A283C.jpeg
 
fxvr5 said:
His arguments require actual pressure measurements. If one does not have that, it's just speculation.

We don't know what his "experience" is. It might or might not pass a smell test. I'm not inclined to buy into that from some unknown poster on a forum. Regardless, it requires actually measuring pressure.
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Yes, I understand about the merits of experience and the perils of forum info.

Knowing a bit about bell curves, I made an assumption that his posit could be something to use, but then, as I've said, I certainly never thought to use SD for pressure determination and hope I never see data looking like that.

I'm not sure how an ordinary reloader would obtain actual pressure info. We have limited tools at our disposal to use in order to guess-ta-mate pressure, and those include cartridge condition and chrono data. Assuming +/_ .5% accuracy with a chrono, if our data near matches factory test info then we've done about all we can. I certainly don't have stain gauges.

Do you have a method for determining pressure outside of basic ballistic calculation? I'd certainly be interested.
 
lordpaxman said:
Please do. I agreed with most of ID’s post with the exception of #2, SD. There are a lot of variables involved with reloading, and even a few with taking chrono measurements that can attribute to higher SDs. I can see if you had a test ladder set up and SDs were tracking and then one ladder had a 5-10X jump maybe something is off but it’d be hard to relate it to pressure.
I use my pistol SD numbers to give me some confidence when I’m at the chrono stage and randomly select 7 rounds from my production run I’m not going to be told “You’re shooting the match for fun, son...”.
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I looked at his hypothetical data which he said was based on his experience and started thinking in terms of percentages. In his first string, 25% delta at the jump, in his second, 50%, and in his third, 70%. But, in the end, I really have nothing to judge the actual worth of it.

And, I think chrono velocity data is a great tool. In a rifle, if I was pushing velocity, I'd have a magnifier, a set of mics and a depriming unit with me as well. The mics to check the case head and the deprime unit so I could look at the actual primer shape out of the pocket. And, bolt resistance. But, handguns especially pistols be another breed. :)
 
denton said:
For the benefit of those who do not believe that peak pressure predicts/drives muzzle velocity, ...
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If your graph was a straight line, your 99% claim of peak pressure driving velocity might be believable. But it's not. I'd say there is 90-95% correlation, which is still very good.

But that is for one set of components in a specific firearm. Proof of your ultimate claim would require similar data for a variety of firearms/barrels from different sources of the same length.
 
Actually, peak pressure accounts for 99.01% of the variation in muzzle velocity in the data shown in the earlier graph, leaving less than 1% of variation to be explained by other sources. The ANOVA table for the data is shown below. As I said, I have replicated this multiple times in different rifles. It always comes out the same. For a given firearm, powder, and bullet, peak pressure is very highly correlated with muzzle velocity.

And, BTW, I did have at least a small hand in designing the PressureTrace mentioned by jmorris.

148282.gif

If you want to generate your own data without hemorrhaging cash, or even going to the range, you can use QuickLoad. It gives a very good estimate, and will confirm what I have said.
 
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