8x57 Pressure Testing

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For several years I have been doing pressure testing mostly revolving around heat treating and metallurgy in regards to Mauser actions. This fall I wanted to run some more standard numbers and look at several variants regarding pressure curves and velocities. This is part of a larger project, but I need a base line for comparison first.

For testing I built a rifle using specially selected components. The action is a Steyr Chilean contact 1912 receiver and bolt. I used these two because I knew exactly what the composition of the steel was and I could have them heat treated to exactly my specs. The receiver was heat treated to 45-50 Hrc and the bolt to 55-60 Hrc. This is the HIGH end of where you would want to heat treat an action. I wanted it on the cusp of being too hard. (Note – HRC is not correct for case hardened actions, these numbers are converted from Superficial for relevance)

The barrel for this project I selected to use a NOS Yugoslavian 8x57 barrel. I fit the barrel to the receiver with what some call “negative” headspace. That is, the bolt will not close on a GO gauge, but will close on ammunition, albeit tightly on crap ammo like Turk. The barrel was also slugged and the bore/groove numbers documented. The chamber was measured using Mauser’s method of measuring with gauge balls to measure for chamber growth. Being that it is a Yugoslavian barrel it measures 23.150” in length.



The chamber was measured using Mauser’s method of measuring with gauge balls to measure for chamber growth. Something I have found fascinating about metallurgy and headspace, most rifles with excess headspace, appear to be a result of chamber growth. This measurement allows me to verify expansion from an over pressure event. With this particular testing, I won't be doing any over pressure instances, but I like to measure and have a baseline just in case.



To measure the pressure a Pressure Trace II is used. This system uses a strain gauge to measure the flex of the barrel and calculate the internal pressures. This system has been a lot of fun to use and to learn. When I was doing destructive testing I ran into several issues and had several long conversations with the man who created and built these systems. He was initially shocked and seriously concerned at what I was doing, because I was doing exactly the opposite of what any safe and sane person would do. After we talked for awhile we identified two different issues with my research. First was that the system was not setup to read as high as I wanted it to (80k psi +) and second that the results I was getting seemed to truncated. That is, they should have been showing higher pressure curves but were not. After I eliminated the software issue, I sent more results, which he showed were the limits of the elasticity of the steel.



The gauges are mounted directly over the chamber and using special glue, attached to the barrel. The electrical tape serves absolutely no purpose other than to make myself feel better. Tearing the tiny wires off of a $35 strain gauge mid test is mildly irritating. Careful measurements are taken of the barrel and chamber for the system to use to calculate pressure.

As a side note I am still looking for some Beschusspatrone. There were some on gunbroker for $250/box but I wasn't willing to pay that. A partial box, 3 to 5 rounds is really all that is needed, but I would buy a full box if someone has one they would like to sell.

Here are some previous test results from July of 2022.

Same action, but using my "Test Barrel 1" which was a somewhat worn K98k barrel.

Turkish 150gr 1940 head stamp

Olympic Greek 198 gr FMJ

PPU 196gr Soft Point ammunition

FN 36 5 head stamp

Yugo 1978 nny


A few comments on the results. First thing most of you will notice is the low pressure readings. This is due to several factors. The system is VERY precise, and as they say, garbage in, garbage out. Not that these results are garbage, but that the results are likely skewed from my inexperience. When I shot these tests and talked to the gentleman who made the system he told me how to add a corrective factor to make them more correct. Not knowing *exactly* what was correct, I left them be. If we use the Greek commercial as our baseline, at ~ 42k PSI, then we can assume that we can add approximately 15k to the numbers. HOWEVER. Test barrel 1 is worn, it is not a new bright crisp barrel. It is possible that the difference in pressure is, at least in part, due to the wear on the throat, lands, and grooves of the barrel. One could further extrapolate the surplus FN and Yugo numbers and come up with a approximate "fudge factor" but that's not very scientific. This is the unknown variance is the reason I left it be. This is also why I am using a new barrel for this new batch of tests.

Elasticity of Steel

When I was working on my mechanical engineering degree I reached a point that I just couldn't stand the theory anymore. I frequently joke about a marvelous electrical engineer that I took several semesters with. He was a certified genius, could show you things that I never could grasp. However, he couldn't wire a light switch to save his life. My strength of materials professor struggled with nearly every aspect of the class, especially steels. He could name 1000 different aluminum's. I'm not going to delve into the finer points of elasticity of steels, other than to say that it was problematic historically, and it is problematic now. Theory often does not hold up to application. Sometimes the inverse of what is rational is true. Truth's aren't always factual. Since this isn't a philosophy course, I will stop there.

If you'd like to delve deeper, you can read some here, this is about as good of a concise online source as I have found.


Why is this relevant? Well, in short, because of how the strain gauge works. It works by measuring the tiny bit of expansion found when the barrel expands due to the forces generated in the chamber. Introducing yet another variable, different steels have different modulus ('s? i?). My above example of variances is also subject to the elasticity of the steel. This issue was really brought to light when I did some initial testing of a Gewehr 88 for over pressure.



Here are what the results look like shooting Yugoslavian 8x57 with a .323 bullet through a rifle with a ".318" bore. The flat lines are the program peaking due to the steels modulus.

Initial Testing

For the first round of tests I have an assortment of commonly found ammunition currently found or recently found on the market. Some of them are the SAME ammo run in the previous tests so that I have multiple comparisons for the new barrel. Another variable that does effect pressure is the case wall thickness. Most of the ammo I measured ranges from .015 to .020. I had originally intended to go back through and edit each to its correct dimensions, but technology being what it is, my computer refuses to connect to the pressure trace unit because it's monday. Or tuesday. Or the first week of the month. Or god knows why, it just didn't feel like it.

While I am ridiculing technology, my friends fancy LabRadar decided it did not want to work at all while on the range, except randomly. So there are only a few velocity measurements.

Turkish - 154 gr 2491 fps

Turkish always causes a certain amount of consternation and this is not necessarily unfounded. As a young man we shot literally thousands of rounds of Turkish ammunition through mostly bolt rifles, but some Hakim’s, and FN 49’s. We never had a catastrophic failure, and other than some dud’s depending on the case, for the most part the ammo was good. However, testing this ammo has shown that it has some tendencies which could be problematic. More on that later.

Because I still have lots of Turkish 8x57, I use it for two different functions. First is initial setup and testing of the pressure test unit. When first setting up, there are always a few of test shots that need made to verify function and communication from the strain gauge to the Pressure Trace unit and from the unit to the computer. Second is Turkish has hilarious pressure curves which will undoubtedly allow me to verify that the unit is reading peak pressures.




Olympic Greek - 198gr

Several years ago at an auction I bought a bunch of “Olympic” Greek manufacture 8x57. This ammo is berdan primed, and uses a 198 gr FMJ. Initial testing showed that it was consistent and low pressure. The box states 2940 bar or 42641 PSI, which gives me a relative starting point, and a consistent baseline. This allows me to double check results each time I setup and test and acts as a “standard”. At some point I will get a load worked up with components to use as my standard, but for now these work.



PPU - 196gr SP - 2212 fps

196gr Soft Point ammunition – a frequent recommendation of commercially available boxer primed non corrosive ammo. While I find the brass to be very soft, and the ammunition generally to be under powered, it is decent ammo.

Yugoslavian Military Surplus – nny 1978 – 198gr bullet. - 2342 fps

The load I'm using is out of my Lyman manual. Its a 150gr Sierra game king over a start load of 47.5gr of h414 and federal 210 match primers. I also loaded 4 with 48gr of powder. I figured it was most likely due to low pressure, because the brass looked fine and only the handloads did it.

Very similar methodology that we used during ammo lot acceptance testing of 120mm tank ammo at APG. Other data we collected was round-to-round dispersion data. All done under ambient, hot and cold temp conditions.

Looking forward to the new results, we always knew ppu was soft shooting, but wow, I didn’t realize it was that low pressure!

Very cool. Looking forward to seeing more.

Any chance of you running some 50s era Yugo? I see that bandied around a lot, and it's the ammo that got me to stop shooting surplus out of good guns.

Cyrano4747 said:

Very cool. Looking forward to seeing more.

Any chance of you running some 50s era Yugo? I see that bandied around a lot, and it's the ammo that got me to stop shooting surplus out of good guns.

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I don't have any 50's Yugoslavian, but I will work on getting some.

FN Military Surplus –
31 3 - 2093 and 2105 fps

36 10 - 1 dud

36 11

37 6

Romanian Military Surplus – 22 72 – 155gr bullet 2288 fps

German Military Surplus
P S * 67 35

Unknown - German? - LD 39 18 - very hard to open bolt

Unknown - German? - LD 39 20 2145 fps

French Military Surplus
Garbage

Greek PCH 1939 Military Surplus

Looking at the different ammunition a few things to note.

As mentioned I hate blue tooth. For whatever reason the Pressure Trace unit has decided to boycott connecting to my desktop which prevents me from editing any of the different factors. One of the factors I wanted to edit was the case wall thickness of the brass. This can effect the pressure, not a lot, but significantly enough it would be nice to have it "right". So that adds a slight margin of error.

Some will note that the ambient conditions are not correct. I found that this had little to do with the effective pressure and so didn't bother with altering them. The barrel was pretty consistently at 130-140 degrees through the course of testing, so to me that ambient temperature is useless anyway.

Keep in mind this is statistically a VERY small sample size, with the samples histories being entirely unknown.

When comparing the initial testing of the Greek Commercial (our "standard" calibration) in the worn barrel vs the new barrel, you can see the pressure in the new barrel is about 3k psi higher.

I left the data un altered in terms of "correction" mainly because based on all the variables I don't KNOW what to correct to. At one point I contacted a few ammunition companies to try and purchase some calibration rounds, but I couldn't even get someone on the phone that had a clue what I was talking about. Looking at the data, using the 42k pressure of the Greek Commercial, I would say add 10-12k psi to all the readings.

What that means is that most of the surplus is in the 50-60k psi. With some of the German at the top end of that range.

The French Garbage as I called it, was due to Duds. We had a small sample, I think I had brought 6 rounds to the range with me, 2 or 3 had duds.

Note LD 39 18, the bolt was very hard to open, but was not the highest pressure noted. In a different experiment I showed that the "flattened primer" rule of thumb is useless and incorrect.

LD 39 20 has the weird spike and flat line which unfortunately isn't anything interesting. The strain gage disconnected due to recoil.

Something else that is interesting when shooting a wide variety of ammo is noticing the report, the flash, and general huge variety between the ammo.

It would be interesting to have commentary from a ballistician, someone that knew internal ballistics better. To me, all of this ammo would be safe to use in any K98k, though some may be more preferable than others. I know based on these results when I find Romanian steel case in the future I will definitely be buying more of it. It has by far the most consistent pressure curves and a surprisingly low pressure. 2300 fps for a 155gr isn't anything to write home about, but I wouldn't hesitate to shoot it in anything chambered for 8x57, and that includes 1893's, 1888's, etc.

Fal Grunt said:

I don't have any 50's Yugoslavian, but I will work on getting some.

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Oh hell I just assumed you had a bunch. PM incoming.

Regarding your issue about determining pressure differential... In the large caliber case I alluded to in my previous response we also installed three copper crusher gages in the powder bed inside the case. The average of those readings were compared to other collected pressure data. Not sure how the small arms community determined similar pressure data. I think they drilled/tapped a pressure sensor into the barrel.

Agree that it would be good to have access to an interior ballistician. The go to guys for small and medium caliber in the private sector was H P White labs. I just checked and they are closed.

Fal Grunt said:

As a side note I am still looking for some Beschusspatrone. There were some on gunbroker for $250/box but I wasn't willing to pay that. A partial box, 3 to 5 rounds is really all that is needed, but I would buy a full box if someone has one they would like to sell.

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The Beschusspatrone is already 30% overpressured from the factory, it would be interesting to know how much the pressure has increased after 80 years of storage.

flynaked said:

Looking forward to the new results, we always knew ppu was soft shooting, but wow, I didn’t realize it was that low pressure!

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I read that a lot in the forum. On the European market we have PPU ammunition 198gr. FMJ BT and Sellier & Bellot ammunition is also very common. Reloaders don't like S&B cartridge cases because they are very brittle. PPU cartridge cases on the other hand, are very popular. The PPU has a hot load here and everyone who has shot my K98ks has complained about it so far.

Stephan98k said:

I read that a lot in the forum. On the European market we have PPU ammunition 198gr. FMJ BT and Sellier & Bellot ammunition is also very common. Reloaders don't like S&B cartridge cases because they are very brittle. PPU cartridge cases on the other hand, are very popular. The PPU has a hot load here and everyone who has shot my K98ks has complained about it so far.

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So to my knowledge. As far ammo sold State side.
Ppu labeled 8mm Mauser is on the "soft" side
Ppu labeled 8x57 IS. Is a standard load. So comparable to S&B.
All according to PPU website. I wouldn't go off any other site most seem to copy/paste info and get it wrong.

you might be able to use Gordon's reloading tool and Vihtavuori N150 powder and put in your correct Case Volume cartridge over all length and tune it via a chronograph to make a pressure calibration loading, N150 in Gordons reloading tool is pretty much spot on to reloading manual values with standard CIP case volume and reloading manual COAL for the given bullet, so i assume that pressure given by Gordons reloading tool is with in a few percent at most