How do you calculate pressure?

[TEXASJake]

I am loading some bullets for my .44 Special revolvers.

I have a few recipes .... I am starting with ...

240 Grain Hard Cast Coated "Keith" style Semi Wad Cutter.
I am loading that over 7.0 grains of Alliant Power Pistol
Using a standard Large Pistol primer (I have several brands but good volume)

Now, question is, how do I calculate pressure? I am looking for a good all-around load that will not stress out the model 24-5, 29-9 or 21-4. I am sure all of them will take whatever I put in them but would be nice to be able to calculate pressure.

I know the "max" pressure is 15,500 psi (107 MPa). I would prefer not to max things out all the time + I want something that I can shoot comfortably for weekly range time. I plan to load up some 200 grain over Trailboss as I have a few pounds of that. but I have 9 pounds of Power Pistol I acquired and would like to find a good use for it.

 

[DWalt]

About the only way to “calculate” chamber pressure is to buy the Quickload software. And I am not too confident about its accuracy. Otherwise, the only alternative is to consult reloading manuals which publish lab-measured pressure information. Measuring pressures yourself would be prohibitively expensive for the equipment required.

The load you mentioned should be very safe in any modern revolver. Power Pistol is in the same category as Unique or Clays Universal. You should be able to find tons of reloading recipes for those propellants.

 

[reddog81]

Use published reloading data and go by the pressures listed.

 

[Nevada Ed]

You can use Power Pistol in a lot of calibers.

However, it is for medium to full loads do to its makeup.

Have fun.

 

[s&wchad]

How do you calculate pressure?

You don’t.
You go by published date that was determined with the proper equipment.

 

[rockquarry]

Use paper published load data from reputable sources like powder and bullet manufacturers or Internet data from the same sources. Dubious data (Internet forums, You Tube, etc.,) without a pedigree may be okay, but it's hardly worth taking a chance.

Checking the velocity with a chronograph and comparing it with more than one source of reliable pressure tested data is far from exact. However, it's close enough to keep you out of trouble if you have at least a good basic handloading background.

 

[Sevens]

These are modern N-Frame revolvers built with the same steel, same heat treating and same tolerances as S&W .41 and .44 Magnum revolvers.

-ANY- .44 Special handload from a solid, known published source is going to not even get to half of the safe and typical peak pressure design scope of your .44 Special revolvers.

QuickLoad is amazing prediction software but it’s reputation is far closer to “accurate” with bottle neck rifle rounds and also with well-practiced users that are astute with the software and how to manage it.

That you’d like to know pressure is admirable but it’s just not exactly feasible. The good news is that you really truly are working with a capable platform. You could look at your level of concern as being much like loading only .38 Special handloads and only shooting them from .357 Magnum revolvers.

 

[TXBryan]

You can't

Agree with those who've forwarded that "you don't" measure pressure. Unless, of course, you want to invest large amounts of money in some very sensitive/sophisticated equipment and a controlled environment to measure combustion.

If you do not own a chronograph buy one. Sounds like you may have one and that's the best guide normally available to handloaders to ensure we're staying within safe pressures. If your velocities mimic the load manuals for given loads you're good to go.

It has always intrigued me that a fair number of handloaders skip the chronograph part of the reloading process. When working up anything like new loads running them over the chronograph is critical to knowing you're on the right track.

"Pressure signs" are generally a vague and uncertain method to ascertain excessive pressure. Guessing is not a good plan.

 

[Jaco1234]

Use a special breach designed to hold high pressure.
Place a measured copper slug in the out put of the breach and screw a specially designed plug behind it. Set off the charge. Then measure the deformity. Of the copper plug.
There are too many variables gun to gun and within a particular powder to do an accurate calculation.
If you are loading Trail Boss, you are staying well under max loads.

 

[Forrest r]

I use a lot of pp in 44spl cases using 200gr to 250gr cast bullets. I typically use 8.0gr of pp.

A "max" load of pp is 240gr cast swc (keith)/8.0gr of pp 15,500psi
Alliant Powder - Reloader's Guide

Brian pearce came up with the same data as alliant.
http://www.goodrichfamilyassoc.org/44_Special_Articles/Brian Pearce on the 44 Special.pdf

A 15,500psi load would have 1 heck of a time maxing out any of the pistols you listed.

 

[DWalt]

Use a special breach designed to hold high pressure.
Place a measured copper slug in the out put of the breach and screw a specially designed plug behind it. Set off the charge. Then measure the deformity. Of the copper plug.
There are too many variables gun to gun and within a particular powder to do an accurate calculation.
If you are loading Trail Boss, you are staying well under max loads.

You might find that method used in some third world country. Nearly every ammunition manufacturer today uses quartz piezo gauges, and has for quite awhile.

 

[Biggfoot44]

I don't know if they still do , but at one time Ohler offered a Strain Gage set up that was only " medium expensive " . Strain gages don't accurately give exact pressure numbers , but can measure relative pressures between different loads . For example , compare your handloads to baseline of factory loads .

But yes , your proposed load is moderate , and well below the capabilities of all those Revolvers .

 

[Paul in Nevada]

A chronograph is the poor man's pressure lab.
If you follow published load data and compare your results against a chronograph, you know if your loads are matching the published data. Beyond that, you have no scientific way of testing pressure on your own. You can try reading primers but the 44spl is a low pressure round. High pressures and low pressures exhibit many of the same marks on a primer but for different reasons.

 

[Nevada Ed]

I loaded rifle and revolvers for 44 years with loads from powder puffs to
a little over, what the manuals listed as a maximum load.

Then in 2010,I bought a chrony.

It was nice to see the FPS of my loads, and I even backed off a few !!

It really came in handy for my shotgun loads, when I was shooting in
ATA trap meets, to have "Legal Loads".

If you want to push the envelope, you really need to have a chrony, to
keep you out of harms way.

"Eyeballing" has yet to become a science and proven to be 100% correct.

 

[WR Moore]

Use a special breach designed to hold high pressure.
Place a measured copper slug in the out put of the breach and screw a specially designed plug behind it. Set off the charge. Then measure the deformity. Of the copper plug.
There are too many variables gun to gun and within a particular powder to do an accurate calculation.
If you are loading Trail Boss, you are staying well under max loads.

As described the above skips a few steps that involve the careful manufacture of the copper slug and qualification of the production lot for amount of deformation at given pressures.

I've got a sneaking suspicion the DOD still uses the copper crusher system on the big guns. It'd be too much trouble to rewrite all those technical manuals and specs.

 

[DWalt]

Actually, the US military began using piezo pressure gauges for artillery prior to WWII, before they became widely used for small arms. When I worked at Hercules in the mid-1960s we were using piezo gauges, but the instrumentation was very crude compared to what is available today. No computers back then. I have written about my experiences at Hercules with pressure measurement here some years ago.