Calculating Chamber Pressure

[rodneymoncrief]

Do any of you guys know which apps or software is best for calculating chamber pressure in rifle cartridges?

 

[g0rd0]

sorry, I am old school I use a Prowley slide rule for that

 

[Ridgerunner665]

Don't really know if its the "best" or not....but QuickLoad seems to work pretty good.

 

[Lefty7mmstw]

Get a strain gauge... any software is going to be an educated guess as it cannot predict some of the variables such as your rifle's bore drag and your ammo's neck tension exactly. I don't use a strain gauge at present but have used one and they are good for what they do. Not at all difficult to set up either if you are careful.

Rifle Chamber Pressure Testing Software & Load Analyzer | Pressure Trace

 

[Mikecr]

Keep in mind though, a strain gauge still has to be calibrated/cal validated, just the same as software(like QL).
I don't know how many people out there actually have the capability/resources to do that.

 

[MagnumManiac]

If you want to predict chamber pressure, then Quickload is the easiest to use.
If you want to measure actual chamber pressure, do what I did and buy the Pressure Trace II system.

Mikecr,
Why do you say that a strain gauge has to be calibrated?
What do we 'calibrate' it to?
SAAMI uses "reference ammunition", we do not have access to this, and factory ammo can be ANY chamber pressure below maximum. All factory ammo I've tested, except a 300WSM, were well below maximum pressure. The 10 shots from a 300WSM were above maximum pressure, the average was 67,000psi, rounded down. If this stuff was precise, even SAAMI wouldn't have to use reference ammo, and then use correction factors to get the same pressure reading as the reference ammo barrel.
This system measures actual chamber pressure in PSI, there are no fudge factors, correction factors or other erroneous calculations, it is what it is. If you make an error in ANY of the variables you use to calibrate the calculating system, such as the diameter of the barrel around the chamber, you WILL get false readings.
I have found it a wonderful tool, and at $26 per rifle to glue on another piezo electric tab, it is quite cheap to use.

Cheers.
gun)

 

[Mikecr]

Well it sounds to me like you're calibrating pressuretrace -with parameters and math, like QL.
What you see with it until actual, and confirmed, is relative.

I'm not suggesting anything is wrong with pressuretrace, or QL, just that it's very hard to know actual pressure. The question is about 'calculating' pressure, and I think QuickLoad's accuracy is as good as you'll get there. Pressure trace does not calculate or predict pressure. It measures expansion and applies math to convert expansion to pressure. Right?
What I believe is that relative peak pressure from both methods are good enough,, that 'seeing' the curve with PT is useful, but not necessarily more accurate than QL. Remember QL math has been validated with test barrels/ammo, and we validate the predictions with our MV measure.

Are the inputs and calcs easy with PressureTrace? Well, given that most people here cannot use external ballistic software very well, it's hard to imagine they would do any better with internal ballistic software.
I'm sure it's accurate only in the right hands.

 

[Lefty7mmstw]

Mike, keep in mind the error carries across the board and is not only applicable to handloaded ammo. Factory ammo will give you a red line not to cross as to pressure levels. I am more interested in uniformity and a normal pressure curve than running to the edge so a thousand or so psi off is of absolutely no consequence. If you think you need to run on the edge than you probably need a bigger chambering.

 

[Mikecr]

Not sure what your gettin at. Factory ammo is no different than reloaded in that it will produce different pressures in different barrels. So while there may be 'standard' factory ammo, our barrels are not their test barrels.
I never said anything about what pressures to run.

Personally, I care about pressures only w/resp to 'problem' pressures, and these are barrel and reloading component specific(local, lot). My reference as to what my pressures are is QL, once calibrated to match my MVs from an Oehler. This pressure may not be exactly right, and it doesn't matter I guess. But I do try to keep my muzzle pressures below 10kpsi(per QL), and I've based a cartridge design of mine on QL predictions that happen to turn out right on the money velocity-wise.

My standards for 'pressure problems' are considered at the range with testing. Where I have a problem, it really doesn't matter how accurately I could predict that point in Kpsi -it's a problem.
Where I don't have a pressure problem, again, it doesn't matter -it's not a problem.

Anyway, the question of 'calculating' chamber pressure(as opposed to measuring) has not been resolved yet.

 

[MagnumManiac]

Thanks Mikecr, get your point.
Pressure Trace is simple to calibrate to each rifle if you measure everything accurately, just as you would for Quickload. Erroneous results can only happen when the inputed data is wrong.
I like the fact that I can measure exactly what pressure I'm getting for individual loads, then re-test with different components to see what changes. I guess Quickload does the same, but I didn't see a different set of parameters on Quickload for different brand primers, maybe I just didn't see that bit when I was messing around with it. It's still on my PC that's cactus.
Both Quickload and the Powley use the same algorythms, as far as I understand their ooerating systems.
The one thing I don't get with Quickload, is why does it require you to input the actual velocity, then jiggle the parameters to match up, shouldn't it predict the velocity pretty closely if all the info inputed was accurate?

Cheers.
gun)

 

[Ridgerunner665]

Copied and pasted from a post of mine on another forum...didn't wanna retype it all...covers a couple of questions asked.

QuickLoad is great.

But only if you take the time to learn and understand how it works, why it works....and most importantly, what makes it work (accurate input).

It is infinitely adjustable...it can be made to exactly match your gun, your batch of powder, your batch of bullets, etc.

But you have to take the measurements and do the math and enter that into the program....if you just turn it on, pick a round, a bullet, and a powder...it might be close, or it might not...but if you do your homework, it can save a lot of wasted components and time.

Is it simple to use? No...not really, not if you use it to its full potential...but I find it addictivly interesting, and have spent a good number of hours just tinkering with it.

Measure and manually enter everything...bullet length, boat tail length, the different bullet diameters, case capacity, case length, seating depth, etc....then get chrono readings...from there you tweak the powder burn rate (they all vary some from lot to lot, and also in different rounds)....mine will match the chrono within 15 fps every time, with my wife's 270, using my current batch of brass, bullets, and powder, and I saw visual pressure signs (very slight ejector marks) at QuickLoad predicted 68,300 psi...that's the only rifle/powder lot I've fully mapped out in the program so far....but I am almost done with my sons 30-06, so far everything is tracking perfectly....its worth noting, I'm using the same powder in both those rifles (H4350), but its burn rate is different in each.

For those that doubt the ability of an algorithm to predict internal ballistics...algorithms can and do predict far more complex things than internal ballistics...and they do so accurately, but only if they have accurate input.

Another common complaint about it....primers...it doesn't need a setting for primers...primers can be accounted for with the powder burn rate.

QuickLoad is very good at what it does...but its not perfect (nothing is)...powder burn rates vary from lot to lot, thats just a fact of life.

Thats why everything is adjustable in QL...one example I've came across...Norma MRP powder, QL says it heat of explosion is 4,020...Norma says its 3,873...bulk density doesn't match either (I forget the numbers for that one)...those things greatly affect the outcome, on the order of 5 grains difference in a 280 Ackley...which one is right? Probably both (or neither one, depending on how you look at it)...for the same reason we have to start over with a new lot of powder...no 2 lots are exactly the same...and also, the different lots were tested on different equipment.

Until there is a powder that is the exact same in every round and for every lot...QuickLoad is the best we have...not knocking pressure trace, they both have their place and do what they are designed to do....but neither of them are a "1 click" simple fix...both require some groundwork.

As to the semantics of the question that was asked....in my opinion...QL "calculates" chamber pressure based on powder burn characteristics that have been measured in sophisticated equipment.

Pressure trace "measures" chamber pressure...but it too is relying on off site measurements to make its magic...that being, the strength of the steel...which also varies some from lot to lot.

Neither system can be 100% right all the time...both can be very close most of the time (with proper specific input)

 

[Mikecr]

The one thing I don't get with Quickload, is why does it require you to input the actual velocity, then jiggle the parameters to match up, shouldn't it predict the velocity pretty closely if all the info inputed was accurate?

There is no way to input all the factors accurately until determined with testing. This, with either QL or PT. We guess to begin.
Also, there is nothing predictable about primer-powder ignition today. A change in flash hole makes a big difference, load density, temperature, primer seating/crush, pocket tightness, striker forces, brand to brand differences, lot differences.

I agree fully with what Ridgerunner665 posted.
Just consider how many ways a 'load manual' could be wrong, and then how advanced QL is w/resp to load manuals. We're very lucky to have as much.

 

[Deleted member 46119]

I finished my 338/26 Nosler and it's shooting.

Load work was done with QL, sanity checked to 'similar' chamberings.
Velocity predicted was 99.98 of measured by MagnetoSpeed.
I have confidence in the QL predicted pressures.

I will be hooking a PT II up to it.

I have an event coming up this week so it will take me bit make the loads, to read the manual and install the gauge. I am looking forward to comparing QL predictions to PT readings.

 

[Mikecr]

Thanks Fred. The information will be valuable to us for sure.