27x145B Mauser pressure test?


Shown on the site "big-ordnance.com is this 35x228 case used for a pressure test round. It shows a small square notch cut in the rim, and says there is a hole drilled in the case.

I have a uK made steel cased 27x145B Mauser round, with an identical notch, and hole 90mm up the case wall from the base. There is also a bare patch on the grey paint on the case where the propellant gas appears to have seeped out of the hole. Was this a pressure test round?

Having said this, I have heard of the concept of a pressure test with a hole in a case before, but what is actually being tested when this is done? The ammunition or the weapon?

My 27x145B case is fitted with a resin projectile, painted black with a red band. I thought this may be a replica, but is has the correct military lot numbers as if it was a real projectile of some sort. Is this projectile also something to do with pressure testing? The markinds are (just above driving band):G DM28 DM1315 LOT RG-50-1



Pressure tests measure the PSI of the case/bullet/primer/powder combination. Proof loads are used to measure the ability of the barrel/receiver to withstand a design pressure.

The case you have could be from a pressure test. I have no way of knowing. In use, the cartridge is inserted into a special chamber that has a hole drilled through it to align with a similar hole in the cartridge case. An apparatus is fitted over it with a close fitting steel piston in line with the hole which is driven upward when the cartridge is fired. This piston, in turn, compresses or “crushes” a copper cylinder, shortening it a certain amount. This shortening is measured and translated into so many pounds per square inch, approximately. (Not actually PSI but Copper Units of Pressure, CUP)

Today, however, most pressure measurements are made electronically with things such as strain gauges which I persoanally think is all black magic, smoke and mirrors.

Unfortunately, there are no direct comparisons which can be made between results from the old copper crusher method (CUP) and the newer strain methods (PSI).

This is really a very simple explanation of the process. It is much more complicated than my military mind is able to comprehend and maybe someone else can tell it better.



Thanks, that explains the process enough for me. I think that may be where my round came from, as it has a hole in the case, notch on the rim, and area around the hole that looks like it was discoloured by hot gases.


I’ve seen this done in many different smaller calibers, but never in the big-bore stuff. Thanks for the info!