7.5 x 55 Swiss Case Max and Min Discrepancy

[RC20]

Not earth shaking but if there is a solid answer.

Wikipedia on Case dimensions shows max at 2.189" (as its not a reload guide it shows no minimum)

Hornady agrees with it a 2.189 max and trim to 2.179

Sierra has it as 2.180 max and trim to 2.170

H and S reflect a trim back normal of .010 but obviously do not agree on the max.

It seems using S is fully safe and gets some lengthen before next trim if its 2.180 max.

[ligonierbill]

I don't have a solid answer on the spec, but I have a little data. I have PPU cases that measure 2.180 new, not any different with one firing. Norma cases are all once fired, but they are even shorter (one measured 2.166). The GP11 cases, however, are over 2.190, also once fired. QuickLoad default case length is 2.188. I hadn't paid attention to this yet, as I have not gone through all my new cases. But I think I will trim to 2.180 just to be consistent.

[Unclenick]

RC20,

Since it is a European cartridge, it is generally best to go to the source of European data (C.I.P.). It says 55.60 mm. Divide by 25.4 for exact conversion and it rounds to 2.189, as the Wikipedia and Hornady suggest. They don't offer a minimum, but I believe they use -0.5 mm as standard. That's -0.0197 inches, very close to -0.020, making the minimum length 2.1693". So nominal trim length would be 55.35 mm or 2.1791 inches. 2.180 is close enough.

I note that C.I.P. drawing was revised just last year (May 16, 2018). I don't know what changed, as I don't have a copy of the previous version, but that one is what European manufacturers will be going by currently.

[RC20]

Unclenick/Bill: That clears it up other than why Sierra was be lower.

I had not thought about it but I have a few GP11 cases I pulled bullets out of (power check and look at the bullets)

I have moved to a bit more trim on the cases to ensure that when I anneal they are still below Max, so the Sierra works fine for the low.

What is funny is that I had to figure out the 25.4 for work as we had brake clutches that were set in metric but didn't have the metric gauges.

I love the digital micrometers you can shift back and forth with. My HP calculator also have a group of metric conversions which is nice (once I shift into centimeters and into more relevant mili meters, it make me nuts but nothing new there (where is the decimal place to go ? I always was more into metric because of artillery size in the various wars (though the Brits with their pounder method was only solved when the internet came into being and you could look it up!)

And the comma thing is odd but figured that out a ways back as well.

[T. O'Heir]

Wikipedia isn't a reloading manual. Anybody can post anything they want there.
Hodgdon shows 2.175" as the trim to length. Max case length is 2.180". That's 55.6mm.
"...don't know what changed..." Quite possibly the plethora of American reloaders loading for Bolt actions and semi-auto's.
"...their pounder method..." Weight of the projectile. Although it confuses the bad guys too.

[RC20]

ToH: Yes I am fully aware of that.

I do know how to compare data and I listed two other sources for that data.

[Unclenick]

Originally Posted by T. O'Heir

Max case length is 2.180". That's 55.6mm

Nope. Sharpen your calculator again. 2.180" is 55.372 mm. 2.189" is 55.6 mm. I wouldn't be surprised if the erroneous data in the load book that have it comes from someone mistakenly entering a conversion factor of 25.5 instead of 25.4. That would account for the 0.009" disagreement.

By the way, 25.4 is an exact conversion. By internationally agreed upon definitions, an inch is exactly 0.0254 m or 25.4 mm. There are no additional decimal places. If you are a math phobic person, online converters abound. Here's one.

Originally Posted by T. O'Heir

Wikipedia isn't a reloading manual. Anybody can post anything they want there.

Nobody took any loading data from the Wikipedia. Just case length, and it turned out to be correct because the author copied it from the C.I.P., as he has for data on numerous other cartridges in the Wikipedia. While it is true anyone can contribute to the Wikipedia, it is also true that anyone can edit anyone else's entry. if you put up anything incorrect that can be readily confirmed by looking it up, your error is discovered by someone else and is corrected surprisingly quickly. Sometimes within a matter of minutes, not days or weeks. There are fact geeks out there cruising the Wiki-universe in search of opportunities to show they know more than the next person by fixing factual errors.

It's important to note that no harm comes from a case being a bit shorter than standard. I knew people who over-trimmed Lake City 7.62 NATO cases on purpose so that they could get through all four reloads their M1A's got out of that military brass without having to trim again. They were shooting matches with loads in these cases trimmed -0.040" below maximum.