[Josh Smith]

Hello Gents,

I'm wondering if there's a publication with factory ammo pressures. For example, if a .38spl is barely +P I'd choose it over a higher pressure +P choice as my revolver isn't +P rated. I also have questions about the Magtech ammo I have loaded in it - it feels no snappier than my standard pressure practice loads.

Thanks,

Josh <><

 

[twoguns]

Mr. Josh,

I am hoping someone does know of such a source, but I don't, sorry. For the most part I get my pressure info off of a company's website, and then usually tend to take it with a grain of salt. There will often be a great difference in pressure readings when taken in a pressure barrel versus an actual firearm, especially a handgun. Unless the website states what platform their round was fired in, it is very hard to trust their pressure figures - in my opinion.

At least most of my reloading manuals will list what platform their data was obtained from when being worked up. I tend to pay more attention to the data that was fired from a listed weapon than I do pressure barrels.

twoguns

 

[oldgranpa]

I doubt anyone has published ammo pressures for factory ammo. First, the pressure is not measured directly, that I know of, since that would be very difficult and probably dangerous. Most testing is done with transducers or strain gages (electronic devices) to measure the resulting stress increase in the steel at the chamber and then a computer calculation for the pressure. This again is difficult and expensive. Some of the bigger ammo companies probably do it for some of their loads, just to insure they meet SAAMI specs. I put a list of SAAMI pressures here in a sticky.
So the easiest method is velocity measurements to get muzzle velocity and knowing the barrel length, etc. the approximate pressure can be calculated.
So your best way to compare ammo is buy yourself a chronograph and do velocity tests. You can compare your numbers with factory numbers that they publish. Almost all the better ammo companies publish ballistic results (velocity, etc.) for their ammo, right here on the internet.

If I'm wrong, someone please correct me.

og

 

[Josh Smith]

Gents,

Thank you.

Josh <><

 

[pff]

Guestimating pressures in an actual firearm is helped by strain gages as OG mentioned. Oeler and others have rigs that do this. By firing loads of known pressure they can extrapolate the data to cover the new load.

A pressure gun uses either a copper or lead cylinder that is held against a piston exposed to the chamber. The cylinder (known as a 'crusher') is compressed and measured; the pressure is computed from a tarage table. This is (or should be) listed as CUP (copper units of pressure) or LUP (lead units of pressure).

Nowadays the labs usually use a piezo transducer mounted flush with the chamber. This not only gives peak but also the entire pressure curve assuming adequate instrumentation. When I used one some years back a storage oscilloscope was used to display the curve.

None of the big factories publish the measured data for each lot of ammo. It varies too much from lot to lot to be meaningful, as they don't use canister lots of powder. They load not to exceed some specified pressure and to achieve the advertized velocity, within limits.

Without getting into statistical quality control (that I don't remember all that well) theory, they basically load to some level that is so many standard deviations below absolute maximum pressure allowed, either SAAMI or their own specs.

[ETA]Sorry for the ramble.......I must be getting OldTimers Disease.

Regards,

Pat

 

[twoguns]

Mr. Josh,

+1 on what Mr. pff said

Mr pfff,

Thank you sir, seriously I did find it interesting and informative. I knew from discussing the 357 Speer Gold Dot load with their customer service folks that they loaded the round to a specific velocity, rather than looking for a magic powder charge. I also knew and they confirmed their powder is a bit different from what I can buy for my reloads.

I may have even read what you were explaining years ago in a reloading manual or reference. But I think you just explained it much more clearly than any book I have read has, so once again, thank you sir (tips my hat).

twoguns

 

[pff]

Most welcome sir.

I suspect that is correct dealing with defensive handgun loads; load to a velocity deemed best for that bullet in a certain barrel whilst not exceeding the pressure limits.

This is one reason why premium ammo is more expensive. The control limits are tighter so they can 'center' the data a bit higher without exceeding the upper control limit. Tighter control limits means it takes longer to get a particular lot into production, and harder to keep it running. An out of limits spot check halts that run til it can be determined where the variation started.

Regards,

Pat